title: SLComposeViewController won't dismiss its parent VC
body: <p>I'm presenting a SLComposeViewController for sending a facebook message. Presenting and posting works fine and the completion block is getting called (all logs are there). </p>
  
  <p>The problem is, when the posting is complete, I also want to dismiss the current view controller (which is presented via a modal segue in storyboard). </p>
  
  <p>I cannot get this VC to dismiss via <code>[self dismissViewControllerAnimated:YES completion:nil];</code> inside the block. </p>
  
  <pre><code>- (void)postToFacebook
  {
      NSLog(@"Posting to Facebook ...");
      if ([SLComposeViewController isAvailableForServiceType:SLServiceTypeFacebook]) {
          NSLog(@"Facebook is available ...");
          SLComposeViewController *fbSheet = [SLComposeViewController
                                                 composeViewControllerForServiceType:SLServiceTypeFacebook];
          [fbSheet setCompletionHandler:^(SLComposeViewControllerResult result) {
              // [self endQuiz];
              [self dismissViewControllerAnimated:YES completion:nil];
              NSLog(@"FB post complete");
          }];
          [fbSheet setInitialText:[NSString stringWithFormat:@"I just scored a %i on this game", self.totalPoints]];
          [self presentViewController:fbSheet animated:YES completion:^{
              NSLog(@"Completed showing FB sheet");
          }];
      } else {
          NSLog(@"Facebook not available");
          [self endQuiz];
      }
  }
  </code></pre>
  
  <p>I've tried variations of block-safe selfs, thinking maybe self was referencing the wrong controller in the block. No luck there, either. </p>