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 Status.CANCEL_STATUS;
			
			synchronized (getLockObject(annotationModel)) {
				if (annotationModel instanceof IAnnotationModelExtension) {
					((IAnnotationModelExtension)annotationModel).replaceAnnotations(fOccurrenceAnnotations, annotationMap);
				} else {
					removeOccurrenceAnnotations();
					Iterator iter= annotationMap.entrySet().iterator();
					while (iter.hasNext()) {
						Map.Entry mapEntry= (Map.Entry)iter.next(); 
						annotationModel.addAnnotation((Annotation)mapEntry.getKey(), (Position)mapEntry.getValue());
					}
				}
				fOccurrenceAnnotations= (Annotation[])annotationMap.keySet().toArray(new Annotation[annotationMap.keySet().size()]);
			}
			return Status.OK_STATUS;
		}
	}	
	
	/**
	 * Updates the occurrences annotations based
	 * on the current selection.
	 * 
	 * @param selection the text selection
	 * @param astRoot the compilation unit AST
	 * @since 3.0
	 */
	protected void updateOccurrenceAnnotations(ITextSelection selection, CompilationUnit astRoot) {
		if (fOccurrencesFinderJob != null)
			fOccurrencesFinderJob.cancel();