title: safeAreaInsets in UIView is 0 on an iPhone X
body: <p>I am updating my app to adapt it for iPhone X. All views work fine by now except one. I have a view controller that presents a custom UIView that covers the whole screen. Before I was using <code>UIScreen.main.bounds</code> to find out the size of the view before all layout was done (I need it for putting the correct itemSize for a collectionView). I thought that now I could do something like
   <code>UIScreen.main.bounds.size.height - safeAreaInsets.bottom</code> to get the right usable size. The problem is, safeAreaInsets returns (0,0,0,0) trying on an iPhone X (Simulator). Any ideas? In other views, I get the right numbers for safeAreaInsets.</p>
  
  <p>Thank you!</p>