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 select previous sub-word action.
		 */
		public SelectPreviousSubWordAction() {
			super(ST.SELECT_WORD_PREVIOUS);
		}
		/*
		 * @see org.eclipse.jdt.internal.ui.javaeditor.JavaEditor.PreviousSubWordAction#setCaretPosition(int)
		 */
		protected void setCaretPosition(final int position) {
			final ISourceViewer viewer= getSourceViewer();
			
			final StyledText text= viewer.getTextWidget();
			if (text != null && !text.isDisposed()) {
				
				final Point selection= text.getSelection();
				final int caret= text.getCaretOffset();
				final int offset= modelOffset2WidgetOffset(viewer, position);
				
				if (caret == selection.x)
					text.setSelectionRange(selection.y, offset - selection.y);
				else
					text.setSelectionRange(selection.x, offset - selection.x);		
			}
		}
	}
	/**
	 * Format element action to format the enclosing java element.