title: _UILayoutGuide bottomLayoutGuide length is zero
body: <p>I encounter a very strange behavior in UILayoutGuide. The bottomLayoutGuide.length returns 0 on messaging the length property.</p>
  
  <p>At the same time printing bottomLayoutGuide in the console returns the following:</p>
  
  <pre><code>&lt;_UILayoutGuide: 0x9ad9c60; frame = (0 455; 0 0); hidden = YES; layer = &lt;CALayer: 0x9ab8200&gt;&gt;
  </code></pre>
  
  <p>It clearly states that the length of UILayoutGuide's frame is 455.</p>
  
  <p>Printing the length directly via</p>
  
  <pre><code>p [((_UILayoutGuide*)self.bottomLayoutGuide) length]
  </code></pre>
  
  <p>returns</p>
  
  <pre><code>(float) $12 = 0
  </code></pre>