title: Error while selecting and deselecting rows in collectionview
body: <p>I have a problem when I quickly <strong>selecting</strong> and <strong>deselecting</strong> rows in my <code>collectionView</code>.
  I have a map and above it i have a horizontal <code>collectionView</code> that i choose what i want to see.</p>
  
  <pre><code>func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
  
          let selectedCell:UICollectionViewCell = collectionView.cellForItemAtIndexPath(indexPath)!
          selectedCell.contentView.backgroundColor = UIColor(red: 102/256, green: 255/256, blue: 255/256, alpha: 0.66)
          switch indexPath.row {
          case 0:
              query0()
              break
          case 1:
              query1()
              break
          case 2:
              query2()
              break
          case 3:
              query3()
              break
          default:
  
              break
          }
  
      }
  </code></pre>
  
  <p>and the code for deselecting is:</p>
  
  <pre><code> func collectionView(collectionView: UICollectionView, didDeselectItemAtIndexPath indexPath: NSIndexPath) {
          let cellToDeselect:UICollectionViewCell = collectionView.cellForItemAtIndexPath(indexPath)!
          cellToDeselect.contentView.backgroundColor = UIColor.clearColor()
      }
  </code></pre>
  
  <p><strong>The error i get is this:</strong></p>
  
  <blockquote>
    <p>fatal error: unexpectedly found nil while unwrapping an Optional value</p>
  </blockquote>
  
  <p>When i tried to selecting slowly the cells i didn't get the error
  But if i do it quickly it crashes</p>
  
  <p>I commented the deselect function and i didn't get any errors (and i check it with quick change of cells)</p>