title: null object reference in ScrollPane/endDrag() when scrollDrag=true
body: <p>In my flash application, I've got multiple windows which use Scrollpanes. The scrollDrag property is set to true on these because I want that functionality. If I close (within my application) one of these 'windows' and open another, I seem to get a whole lot of this error showing up in my logs:</p>
  
  <pre><code>TypeError: Error #1009: Cannot access a property or method of a null object reference.
  at fl.containers::ScrollPane/endDrag()
  </code></pre>
  
  <p>Sometimes I get thousands of these, which I'm guessing is probably slowing my app down a bit, but otherwise is not causing a problem. Looking through the adobe code for scrollpane, endDrag is really simple:</p>
  
  <pre><code>protected function endDrag(event:MouseEvent):void {
          stage.removeEventListener(MouseEvent.MOUSE_MOVE, doDrag);
      }
  </code></pre>
  
  <p>The stage var is the only thing that could be null here.</p>
  
  <p>The only thing I can think to do is set scrollDrag=false before the window in my application closes so that nothing is listening for the event. Any other suggestions? </p>