title: Attempt to present <app.TabController> on <app.ViewController> which is already presenting <UIAlertController> in swift
body: <p>Ok so I'm adding a <code>please wait</code> popup for the operation that takes longer than usual in my ios app.</p>
  
  <p>I have a segue from my ViewController to TabController and when I invoke it like this:</p>
  
  <pre><code>self.performSegueWithIdentifier("openMainApp", sender: self)
  </code></pre>
  
  <p>everything works fine.</p>
  
  <p>But when I surround it with:</p>
  
  <pre><code>let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .Alert)
  
  alert.view.tintColor = UIColor.blackColor()
  let loadingIndicator: UIActivityIndicatorView = UIActivityIndicatorView(frame: CGRectMake(10, 5, 50, 50)) as UIActivityIndicatorView
  loadingIndicator.hidesWhenStopped = true
  loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
  loadingIndicator.startAnimating();
  
  alert.view.addSubview(loadingIndicator)
  presentViewController(alert, animated: true, completion: nil)
  
      self.performSegueWithIdentifier("openMainApp", sender: self)
  
  dismissViewControllerAnimated(false, completion: nil)
  </code></pre>
  
  <p>then I'm getting a warning:</p>
  
  <pre><code>Warning: Attempt to present &lt;app.TabController: 0x7ff6dc00bd40&gt;  
  on &lt;app.ViewController: 0x7ff6d9cf6600&gt; which is already presenting 
  &lt;UIAlertController: 0x7ff6d9d78530&gt;
  </code></pre>
  
  <p>how can I skip this warning?</p>