title: UICollectionView cellForItemAtIndexPath not called after numberOfItemsInSection returns nonzero item number
body: <p>Is there any reason that <code>cellForItemAtIndexPath</code> would not get called after <code>numberOfItemsInSection</code> gets called and returns a nonzero number? Would a <code>reloadData</code> from a completion block affect this? I'm running into an issue in which I am trying to delete a cell through a <code>UIAlertController</code> and the UI looks great, but when I go to <code>reloadData</code> after the UI animation finishes <code>numberOfItemsInSection</code> properly gets called with the right number of elements (the previous number of elements minus 1), yet <code>cellForItemAtIndexPath</code> does not get called, so my cells don't get reloaded. Any ideas as to why this would happen?</p>
  
  <p>This is on <code>Swift 1.2</code>, <code>XCode 6.4</code>, and any help would be greatly appreciated</p>
  
  <p>Just to give a bit more information, the method I'm using to delete a cell is looking a little like:</p>
  
  <pre><code>self.collectionView.performBatchUpdates({
      let indexPathCellToDelete = self.indexPath(feedCell)
      self.collectionView.deleteItemsAtIndexPaths([indexPathCellToDelete])
  }, completion:nil)
  </code></pre>
  
  <p>Would having a second reload in the completion block change anything?</p>