! Address potential threading issue

Author: wmjordan

Diff for: Codist/QuickInfo/QuickInfoOverride.cs

@@ -203,6 +203,7 @@ void RemoveSymbolHighlight(object sender, MouseEventArgs e) {
 				((TextBlock)sender).Background = Brushes.Transparent;
 			}
 
+			[SuppressMessage("Usage", Suppression.VSTHRD100, Justification = Suppression.EventHandler)]
 			void GoToSource(object sender, MouseButtonEventArgs e) {
 				try {
 					_symbol.GoToDefinition();

Diff for: Codist/Semantics/CodeAnalysisHelper.Symbol.cs

@@ -1138,6 +1138,7 @@ public static void GoToSource(this SyntaxReference loc) {
 		}
 
 		public static void GoToDefinition(this ISymbol symbol) {
+			Microsoft.VisualStudio.Shell.ThreadHelper.ThrowIfNotOnUIThread();
 			var r = symbol.GetSourceReferences();
 			if (r.Length == 1) {
 				r[0].GoToSource();