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
int position= widgetOffset2ModelOffset(viewer, viewer.getTextWidget().getCaretOffset());
			if (position == -1)
				return;
			
			int next= findNextPosition(position);
			if (next != BreakIterator.DONE) {
				setCaretPosition(next);
				getTextWidget().showSelection();
				fireSelectionChanged();
			}
				
		}
		/**
		 * Finds the next position after the given position.
		 * 
		 * @param position the current position
		 * @return the next position
		 */
		protected int findNextPosition(int position) {
			ISourceViewer viewer= getSourceViewer();
			int widget= -1;
			while (position != BreakIterator.DONE && widget == -1) { 
				position= fIterator.following(position);
				if (position != BreakIterator.DONE)
					widget= modelOffset2WidgetOffset(viewer, position);
			}
			return position;
		}
		/**
		 * Sets the caret position to the sub-word boundary given with <code>position</code>.