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
protected JavaWordIterator fIterator= new JavaWordIterator();
		/**
		 * Creates a new next sub-word action.
		 * 
		 * @param code Action code for the default operation. Must be an action code from @see org.eclipse.swt.custom.ST.
		 */
		protected NextSubWordAction(int code) {
			super(getSourceViewer().getTextWidget(), code);
		}
		/*
		 * @see org.eclipse.jface.action.IAction#run()
		 */
		public void run() {
			
			final IPreferenceStore store= getPreferenceStore();
			if (!store.getBoolean(PreferenceConstants.EDITOR_SUB_WORD_NAVIGATION)) {
				super.run();
				return;				
			}
			
			final ISourceViewer viewer= getSourceViewer();
			final IDocument document= viewer.getDocument();
			fIterator.setText((CharacterIterator) new DocumentCharacterIterator(document));