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
/**
	 * Returns the lock object for the given annotation model.
	 * 
	 * @param annotationModel the annotation model
	 * @return the annotation model's lock object
	 * @since 3.0
	 */
	private Object getLockObject(IAnnotationModel annotationModel) { 
		if (annotationModel instanceof ISynchronizable)
			return ((ISynchronizable)annotationModel).getLockObject();
		else
			return annotationModel;
	}
	
	/**
	 * Updates the annotation views that show the given annotation.
	 * 
	 * @param annotation the annotation
	 */
	private void updateAnnotationViews(Annotation annotation) {
		IMarker marker= null;
		if (annotation instanceof MarkerAnnotation)
			marker= ((MarkerAnnotation) annotation).getMarker();
		else if (annotation instanceof IJavaAnnotation) {
			Iterator e= ((IJavaAnnotation) annotation).getOverlaidIterator();
			if (e != null) {
				while (e.hasNext()) {
					Object o= e.next();
					if (o instanceof MarkerAnnotation) {
						marker= ((MarkerAnnotation) o).getMarker();