title: Flex 3 Close UrlLoader throws exception
body: <p>I am trying to simulate a 'HEAD' method using UrlLoader; essentially, I just want to check for the presence of a file without downloading the entire thing. I figured I would just use HttpStatusEvent, but the following code throws an exception (one that I can't wrap in a try/catch block) when you run in debug mode.</p>
  
  <pre><code>&lt;mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="init()"&gt;
  &lt;mx:Script&gt;
      &lt;![CDATA[
  
         private static const BIG_FILE:String = "http://www.archive.org/download/gspmovvideotestIMG0021mov/IMG_0021.mov";
  
         private var _loader:URLLoader;
  
         private function init():void {
              _loader = new URLLoader();
              _loader.addEventListener(HTTPStatusEvent.HTTP_STATUS, statusHandler);
              _loader.addEventListener(IOErrorEvent.IO_ERROR, errorHandler);
              _loader.addEventListener(SecurityErrorEvent.SECURITY_ERROR, errorHandler);
              _loader.load(new URLRequest(BIG_FILE));   
         }
  
         public function unload():void { 
              try {
                  _loader.close();
                  _loader.removeEventListener(HTTPStatusEvent.HTTP_STATUS, statusHandler);
                  _loader.removeEventListener(IOErrorEvent.IO_ERROR, errorHandler);
                  _loader.removeEventListener(SecurityErrorEvent.SECURITY_ERROR, errorHandler);
              }
              catch(error:Error) {
                  status.text = error.message;
              }
          }
  
          private function errorHandler(event:Event):void {
              status.text = "error";
              unload();
          }
  
          private function statusHandler(event:HTTPStatusEvent):void {
              if(event.status.toString().match(/^2/)) {
                  status.text = "success";
                  unload();
              }
              else {
                  errorHandler(event);
              }
          }   
      ]]&gt;
  &lt;/mx:Script&gt;
  
  &lt;mx:Label id="status" /&gt;
  </code></pre>
  
  <p></p>
  
  <p>I tried using ProgressEvents instead, but it seems that some 404 pages return content, so the status event will correctly identify if the page exists.</p>
  
  <p>Anyone have any ideas?</p>