Make dialog behave better when canvases have styles applied.

This change sets up the overlays so that the style from the upper canvas
is always used. This prevents bold characters from the lower canvas from
"bleeding through" to the final result.

widgets/dialog/dialog.go

@@ -405,7 +405,9 @@ type IOpenExt interface {
 func OpenExt(w IOpenExt, container gowid.ISettableComposite, width gowid.IWidgetDimension, height gowid.IWidgetDimension, app gowid.IApp) {
 	ov := overlay.New(w, container.SubWidget(),
 		gowid.VAlignMiddle{}, height, // Intended to mean use as much vertical space as you need
-		gowid.HAlignMiddle{}, width)
+		gowid.HAlignMiddle{}, width, overlay.Options{
+			IgnoreLowerStyle: true,
+		})
 
 	if _, ok := width.(gowid.IRenderFixed); ok {
 		w.SetContentWidth(gowid.RenderFixed{}, app) // fixed or weight:1, ratio:0.5