Font leak in DotExportRadioGroupFieldEditor.

[merks]

This error is logged visiting all of GEF's preferences:

java.lang.Error: SWT Resource was not properly disposed
	at org.eclipse.swt.graphics.Resource.initNonDisposeTracking(Resource.java:172)
	at org.eclipse.swt.graphics.Resource.<init>(Resource.java:120)
	at org.eclipse.swt.graphics.Font.<init>(Font.java:80)
	at org.eclipse.gef.dot.internal.ui.preferences.DotExportRadioGroupFieldEditor.getRadioBoxControl(DotExportRadioGroupFieldEditor.java:207)
	at org.eclipse.gef.dot.internal.ui.preferences.DotExportRadioGroupFieldEditor.doFillIntoGrid(DotExportRadioGroupFieldEditor.java:145)
	at org.eclipse.jface.preference.FieldEditor.createControl(FieldEditor.java:248)
	at org.eclipse.gef.dot.internal.ui.preferences.DotExportRadioGroupFieldEditor.<init>(DotExportRadioGroupFieldEditor.java:109)
	at org.eclipse.gef.dot.internal.ui.preferences.DotExportRadioGroupFieldEditor.<init>(DotExportRadioGroupFieldEditor.java:94)
	at org.eclipse.gef.dot.internal.ui.preferences.GraphvizPreferencePage.addDotExportUI(GraphvizPreferencePage.java:238)
	at org.eclipse.gef.dot.internal.ui.preferences.GraphvizPreferencePage.createFieldEditors(GraphvizPreferencePage.java:182)
	at org.eclipse.jface.preference.FieldEditorPreferencePage.createContents(FieldEditorPreferencePage.java:227)
	at org.eclipse.jface.preference.PreferencePage.createControl(PreferencePage.java:244)
	at org.eclipse.jface.preference.PreferenceDialog.createPageControl(PreferenceDialog.java:1433)
	at org.eclipse.jface.preference.PreferenceDialog$8.run(PreferenceDialog.java:1196)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:174)
	at org.eclipse.jface.preference.PreferenceDialog.showPage(PreferenceDialog.java:1188)
	at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.showPage(FilteredPreferenceDialog.java:618)
	at org.eclipse.jface.preference.PreferenceDialog$5.lambda$0(PreferenceDialog.java:660)
	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:67)
	at org.eclipse.jface.preference.PreferenceDialog$5.selectionChanged(PreferenceDialog.java:657)
	at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:820)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:174)
	at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:817)
	at org.eclipse.jface.viewers.ColumnViewer.firePostSelectionChanged(ColumnViewer.java:1065)
	at org.eclipse.jface.viewers.StructuredViewer.setSelection(StructuredViewer.java:1665)
	at org.eclipse.jface.viewers.TreeViewer.setSelection(TreeViewer.java:1092)
	at org.eclipse.jface.viewers.Viewer.setSelection(Viewer.java:375)
	at org.eclipse.oomph.setup.ui.recorder.PreferenceInitializationDialog$Initializer$2$2.run(PreferenceInitializationDialog.java:427)
	at org.eclipse.oomph.ui.UIUtil$7.run(UIUtil.java:662)
	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40)
	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:132)
	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4046)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3662)
	at org.eclipse.jface.operation.ModalContext$ModalContextThread.block(ModalContext.java:168)
	at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:370)
	at org.eclipse.jface.dialogs.ProgressMonitorDialog.run(ProgressMonitorDialog.java:470)
	at org.eclipse.oomph.setup.ui.recorder.PreferenceInitializationDialog$Initializer.run(PreferenceInitializationDialog.java:383)
	at org.eclipse.oomph.setup.ui.recorder.PreferenceInitializationDialog.okPressed(PreferenceInitializationDialog.java:280)
	at org.eclipse.jface.dialogs.Dialog.buttonPressed(Dialog.java:468)
	at org.eclipse.jface.dialogs.Dialog.lambda$0(Dialog.java:619)
	at org.eclipse.swt.events.SelectionListener$1.widgetSelected(SelectionListener.java:84)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:252)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4273)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4071)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3659)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:823)
	at org.eclipse.jface.window.Window.open(Window.java:799)
	at org.eclipse.oomph.setup.ui.recorder.RecorderManager$7.widgetSelected(RecorderManager.java:858)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:252)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4273)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4071)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3659)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:823)
	at org.eclipse.jface.window.Window.open(Window.java:799)
	at org.eclipse.ui.internal.OpenPreferencesAction.run(OpenPreferencesAction.java:64)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:474)
	at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:583)
	at org.eclipse.jface.action.ActionContributionItem.lambda$4(ActionContributionItem.java:417)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4273)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4071)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3659)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1152)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1043)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:152)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:648)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:555)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:173)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:152)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:208)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:136)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:402)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:651)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:588)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1459)