title: Scrolling to the bottom of collectionView does not work
body: <p>I try to scroll to the bottom of the collectionView when the view first loads its items. I run this function inside viewDidLoad:</p>
  
  <pre><code>private func fetchMessages() {
      guard let r = replyTo else { return }
      let urlString = "\(Config.URL)/api/messages/replyTo/\(r)/offset/\(offset)"
      guard let authToken = Auth.getToken() else { return }
      let headers = ["Authorization": "Bearer \(authToken)"]
      Alamofire.request(urlString, headers: headers).responseJSON { (response) in
          guard let value = response.result.value else { return }
          let json = JSON(value)
          for messagesJSON in json["messages"].arrayValue {
              let message = Message(json: messagesJSON.dictionaryObject ?? [:])
              self.messages.append(message)
          }
          self.messages.reverse()
          DispatchQueue.main.async {
              self.collectionView?.reloadData()
              let indexPath = IndexPath(item: self.messages.count - 1, section: 0)
              self.collectionView?.scrollToItem(at: indexPath, at: .bottom, animated: false)
          }
      }
  }
  </code></pre>
  
  <p>I get the last indexPath, and then use scrollToItem to scroll to the bottom, but it does not want to scroll to the bottom. It does not scroll at all. Everything works except for the scrolling.</p>