title: PHVideoRequestOptions' progressHandler not called
body: <p>When I'm loading video from iCloud, I'd want a UIProgressView to be updated about the progress. For some reason, progressHandler doesn't get called. I've tried to do it like it's done in <a href="https://developer.apple.com/library/prerelease/ios/samplecode/UsingPhotosFramework/Listings/SamplePhotosApp_AAPLAssetViewController_m.html#//apple_ref/doc/uid/TP40014575-SamplePhotosApp_AAPLAssetViewController_m-DontLinkElementID_10" rel="nofollow">SamplePhotosApp</a> (which loads images though), but can't get it working.</p>
  
  <p>Here's the code I use for options and requesting the video:</p>
  
  <pre><code>    let videoRequestOptions = PHVideoRequestOptions()
      videoRequestOptions.deliveryMode = .FastFormat
      videoRequestOptions.version = .Original
      videoRequestOptions.networkAccessAllowed = true
      videoRequestOptions.progressHandler = { (progress, error, stop, info) in
          dispatch_async(dispatch_get_main_queue(), {
              print(progress)
              self.progressView.progress = Float(progress)
          })
      }
  
      PHImageManager.defaultManager().requestPlayerItemForVideo(asset, options: videoRequestOptions, resultHandler: {
          result, info in
          self.videoPlayer = AVPlayer(playerItem: result!)
      })
  </code></pre>
  
  <p>This code won't even print anything, so it looks like the progressHandler block won't be called at all. The video I'm requesting is in iCloud, because this will crash if networkAccessAllowed is set to false.</p>
  
  <p>Where's the problem?</p>