title: How can I check if an indexPath is valid, thus avoiding an "attempt to scroll to invalid index path" error?
body: <p>How can I check to see whether an <code>indexPath</code> is valid or not?</p>
  
  <p>I want to scroll to an <code>indexPath</code>, but I sometimes get an error if my <code>UICollectionView</code> subviews aren't finished loading.</p>