title: UIAlertController dismiss completion never gets called
body: <p>In the following code, when my web view fails to load, the alert is properly shown with the Retry button, as expected.  The alert goes away when tapping the Retry button, but the completion never gets called.  Why is this?</p>
  
  <pre><code>func webView(_ webView: UIWebView, didFailLoadWithError error: Error) {
      let alert = UIAlertController(title: "Network Error", message: "There was a error loading the page.", preferredStyle: .alert)
      alert.addAction(UIAlertAction(title: "Retry", style: .default, handler: { _ in
          alert.dismiss(animated: true, completion: {
              self.webView.loadHTMLString("Reloaded", baseURL: nil)
          })
      }));
  
      self.present(alert, animated: true, completion: nil)
  }
  </code></pre>