title: ECSlidingViewController crashes on second swipe
body: <p>I'm building a new project using ECSlidingViewController v2.  The first time I swipe to open the left under view, it works great.  But when I swipe the second time, I get an EXC_BAD_ACCESS crash.  The reference is to the NSMapTable in the controller.</p>
  
  <pre><code>- (void)updateTopViewGestures {
      BOOL topViewIsAnchored = self.currentTopViewPosition == ECSlidingViewControllerTopViewPositionAnchoredLeft ||
                           self.currentTopViewPosition == ECSlidingViewControllerTopViewPositionAnchoredRight;
      UIView *topView = self.topViewController.view;
  
      if (topViewIsAnchored) {
         ...
      } else {
          ...
  ---&gt;    [self.customAnchoredGesturesViewMap removeAllObjects];
      }
  }
  </code></pre>