title: UIPickerView height constraint animation jumps
body: <p>I'm animating the height constraint of an UIPickerView.
  The View jumps to a small height still showing 1 row and then animates till height 0.</p>
  
  <pre><code>UIView.animate(withDuration: 0.5, animations: {
          self.timePickerHeightConstraint.constant =    self.pickerIsClosed ? 216 : 0
          self.view.layoutIfNeeded()
      }) { compilation in
          self.pickerIsClosed = !self.pickerIsClosed
      }
  </code></pre>
  
  <p>Any suggestions? 
  Thanka</p>