Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
return -1;
			}			
		}
		public void applyTextPresentation(TextPresentation textPresentation) {
			if (fActiveRegion == null)
				return;
			IRegion region= textPresentation.getExtent();
			if (fActiveRegion.getOffset() + fActiveRegion.getLength() >= region.getOffset() && region.getOffset() + region.getLength() > fActiveRegion.getOffset())
				textPresentation.mergeStyleRange(new StyleRange(fActiveRegion.getOffset(), fActiveRegion.getLength(), fColor, null));
		}
		
		private void highlightRegion(ISourceViewer viewer, IRegion region) {
			if (region.equals(fActiveRegion))
				return;
			repairRepresentation();
			
			StyledText text= viewer.getTextWidget();
			if (text == null || text.isDisposed())
				return;
			
			
			int offset= 0;
			int length= 0;
			if (viewer instanceof ITextViewerExtension5) {
				ITextViewerExtension5 extension= (ITextViewerExtension5) viewer;
				IRegion widgetRange= extension.modelRange2WidgetRange(region);
				if (widgetRange == null)
					return;
					
				offset= widgetRange.getOffset();