title: SFSafariViewController shows incorrectly when pushed in UINavigationController with modalPresentationStyle = .FormSheet
body: <p>I have a simple Settings table view that is the first view of a UINavigationController.</p>
  
  <p>I present the Settings UINavigationController with the .FormSheet modalPresentationStyle, which means on an iPhone it takes up the full screen, while on an iPad, it displays centered modally.</p>
  
  <p>Now I want want one of the rows in the Settings table to push a SFSafariViewController onto the navigation stack.</p>
  
  <p>This works fine on an iPhone, but on the iPad it does not. iPad screenshot:</p>
  
  <p><a href="https://i.stack.imgur.com/isczm.png" rel="noreferrer"><img src="https://i.stack.imgur.com/isczm.png" alt="enter image description here"></a></p>
  
  <p>Note that the part of the SFSafariViewController navigation bar shows underneath the navigation bar (with the Settings back button). See red rectangle in image.</p>
  
  <pre><code>let urlText = "http://www.apple.com"       
  let url = NSURL(string: urlText)!     
  let safariViewController = SFSafariViewController(URL: url)
  self.navigationController?.pushViewController(safariViewController, animated: true)
  </code></pre>
  
  <p>On the iPhone, you don't see the SFSafariViewController navigation bar at all - which is perfect for my use case.</p>
  
  <p>Any magic setting to make this work correctly?</p>