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 (selectionProvider instanceof IPostSelectionProvider)  {
				IPostSelectionProvider provider= (IPostSelectionProvider) selectionProvider;
				provider.addPostSelectionChangedListener(this);
			} else  {
				selectionProvider.addSelectionChangedListener(this);
			}
		}
		/**
		 * Removes this selection changed listener from the given selection provider.
		 * 
		 * @param selectionProvider the selection provider
		 */
		public void uninstall(ISelectionProvider selectionProvider) {
			if (selectionProvider == null)
				return;
			
			if (selectionProvider instanceof IPostSelectionProvider)  {
				IPostSelectionProvider provider= (IPostSelectionProvider) selectionProvider;
				provider.removePostSelectionChangedListener(this);
			} else  {
				selectionProvider.removeSelectionChangedListener(this);
			}			
		}
	}
	/**
	 * Updates the Java outline page selection and this editor's range indicator.
	 * 
	 * @since 3.0
	 */
	private class EditorSelectionChangedListener extends AbstractSelectionChangedListener {