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 null;
			
			
			try {
				fURLString= line.substring(urlOffsetInLine, urlOffsetInLine + urlLength);
				new URL(fURLString);
			} catch (MalformedURLException ex) {
				fURLString= null;
				return null;
			}
			
			return new Region(lineInfo.getOffset() + urlOffsetInLine, urlLength);
		}
		private int getCurrentTextOffset(ISourceViewer viewer) {
			try {					
				StyledText text= viewer.getTextWidget();			
				if (text == null || text.isDisposed())
					return -1;
				Display display= text.getDisplay();				
				Point absolutePosition= display.getCursorLocation();
				Point relativePosition= text.toControl(absolutePosition);
				
				int widgetOffset= text.getOffsetAtLocation(relativePosition);
				if (viewer instanceof ITextViewerExtension5) {
					ITextViewerExtension5 extension= (ITextViewerExtension5) viewer;
					return extension.widgetOffset2ModelOffset(widgetOffset);
				} else {
					return widgetOffset + viewer.getVisibleRegion().getOffset();
				}
			} catch (IllegalArgumentException e) {