title: gestureRecognizer:shouldBeRequiredToFailByGestureRecognizer crashing
body: <p>I have a gesture recognizer on my view controller which I use to slide in/out the navigation bar. Unfortunately there is a bad NSZombie that makes the whole app crash when I go swipe to go to the previous controller. It's very difficult to track because it only happens in a specific view controller.</p>
  
  <p>Here is the error:</p>
  
  <pre><code>[MyViewController gestureRecognizer:shouldBeRequiredToFailByGestureRecognizer:]: message sent to deallocated instance 
  </code></pre>
  
  <p>And here is my code:</p>
  
  <pre><code>- (void)viewDidLoad
  {
      [super viewDidLoad];
      // Do any additional setup after loading the view.
      UIPanGestureRecognizer *pgr = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pgr:)];
      pgr.delegate = self;
      [self.view addGestureRecognizer:pgr];
  }
  
  - (void)pgr:(UIPanGestureRecognizer *)gesture {
      // Check if this is the first touch
      if (gesture.state == UIGestureRecognizerStateBegan) {
          CGPoint point = [gesture locationInView:gesture.view];
          self.start = point.y;
      }
  
      CGPoint point = [gesture locationInView:gesture.view];
      self.currentX = point.x;
      self.offsetY = point.y - self.start;
  }
  
  - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
      return YES;
  }
  
  - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
      if ([gestureRecognizer isKindOfClass:[UIScreenEdgePanGestureRecognizer class]]) {
          return YES;
      }
  
      return NO;
  }
  </code></pre>