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
/**
		 * Creates a new delete next sub-word action.
		 */
		public DeleteNextSubWordAction() {
			super(ST.DELETE_WORD_NEXT);
		}
		/*
		 * @see org.eclipse.jdt.internal.ui.javaeditor.JavaEditor.NextSubWordAction#setCaretPosition(int)
		 */
		protected void setCaretPosition(final int position) {
			if (!validateEditorInputState())
				return;
			
			final ISourceViewer viewer= getSourceViewer();
			final int caret, length;
			Point selection= viewer.getSelectedRange();
			if (selection.y != 0) {
				caret= selection.x;
				length= selection.y;
			} else {