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
if (!redrawAll && viewer instanceof ITextViewerExtension2)
					((ITextViewerExtension2) viewer).invalidateTextPresentation(offset, length);
				else
					viewer.invalidateTextPresentation();
				
				
				if (viewer instanceof ITextViewerExtension5) {
					ITextViewerExtension5 extension= (ITextViewerExtension5) viewer;
					offset= extension.modelOffset2WidgetOffset(offset);
				} else {
					offset -= viewer.getVisibleRegion().getOffset();
				}
				try {
					StyledText text= viewer.getTextWidget();
					text.redrawRange(offset, length, false);
				} catch (IllegalArgumentException x) {
				}
			}
		}
				
		private IRegion selectWord(IDocument document, int anchor) {
		
			try {		
				int offset= anchor;
				char c;
	
				while (offset >= 0) {
					c= document.getChar(offset);
					if (!Character.isJavaIdentifierPart(c))