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
Position[] positions= new Position[matches.size()];
		int i= 0;
		for (Iterator each= matches.iterator(); each.hasNext();) {
			ASTNode currentNode= (ASTNode)each.next();
			positions[i++]= new Position(currentNode.getStartPosition(), currentNode.getLength());
		}
		
		fOccurrencesFinderJob= new OccurrencesFinderJob(document, positions, selection);
		
		
		
		fOccurrencesFinderJob.run(new NullProgressMonitor());
	}
	
	protected void installOccurrencesFinder() {
		fMarkOccurrenceAnnotations= true;
		
		fPostSelectionListenerWithAST= new ISelectionListenerWithAST() {
			public void selectionChanged(IEditorPart part, ITextSelection selection, CompilationUnit astRoot) {
				updateOccurrenceAnnotations(selection, astRoot);
			}
		};
		SelectionListenerWithASTManager.getDefault().addListener(this, fPostSelectionListenerWithAST);
		if (getSelectionProvider() != null) {
			fForcedMarkOccurrencesSelection= getSelectionProvider().getSelection();
			SelectionListenerWithASTManager.getDefault().forceSelectionChange(this, (ITextSelection)fForcedMarkOccurrencesSelection);
		}
		
		if (fOccurrencesFinderJobCanceler == null) {