title: UIButton height is 0 but title is still visible
body: <p>I have an <code>UIButton</code> placed with constraints. In the interface of the view controller I created an <code>IBOutlet</code> for the height constraint of the button. In <code>viewDidLoad</code> method I have the code:</p>
  
  <pre><code>myButtonConstraint.constat = 0;
  [self.view layoutIfNeeded];
  </code></pre>
  
  <p>In <code>viewWillAppear</code> the height of the button is 0, but on the simulator the title of the button is still visible. Even though the title of the button is visible, the button is not tappable, it performs no action.</p>
  
  <p>What is going on?</p>