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/ClipboardOperationAction.java
*/
	public void run() {
		if (fOperationCode == -1 || fOperationTarget == null)
			return;
			
		ITextEditor editor= getTextEditor();
		if (editor == null)
			return;
		if (!isReadOnlyOperation() && !validateEditorInputState())
			return;
		BusyIndicator.showWhile(getDisplay(), new Runnable() {
			public void run() {
				internalDoOperation();
			}
		});
	}
	
	private Shell getShell() {
		ITextEditor editor= getTextEditor();
		if (editor != null) {
			IWorkbenchPartSite site= editor.getSite();
			Shell shell= site.getShell();
			if (shell != null && !shell.isDisposed()) {
				return shell;
			}
		}
		return null;
	}
	
	private Display getDisplay() {