title: UIView's snapshotViewAfterScreenUpdates:, determine if afterScreenUpdates needs to be YES
body: <p>If you call <em>[view snapshotViewAfterScreenUpdates:NO]</em> on a view that hasn't been displayed yet, you get:</p>
  
  <blockquote>
    <p>Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates.</p>
  </blockquote>
  
  <p>This goes away by changing the param to YES, which makes sense. Passing YES has a performance hit, and I don't need "after screen updates" unless it hasn't been displayed yet. Is there a way to know when passing in NO will cause that error, so that I can pass in YES only in that scenario?</p>
  
  <p>I tried <em>[view snapshotViewAfterScreenUpdates:view.layer.needsDisplay]</em>, but that didn't do it.</p>