title: UICollectionViewCell not loading until fully visible
body: <p>I currently have a UICollectionView with cells that contain images which are loaded in the background. On initial load, there are screen sizes where cells are only half visible. The Collection View isn't loading the cells until the bottom is reached, so my table looks empty until i scroll past the bottom edge of the cells. Here's a gif of what I'm talking about:</p>
  
  <p><img src="https://imgur.com/RIozTVD.gif" alt="loading"></p>