title: How to count selected UITableView rows in Swift. Optional in indexPathForSelectedRow
body: <p>I'm trying to get number of selected rows in my tableView:</p>
  
  <pre><code>self.tableView.setEditing(true, animated: true)
  
  tableView.allowsMultipleSelection = true
  
  func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
     updateCount()
  }
  
  func tableView(tableView: UITableView, didDeselectRowAtIndexPath indexPath: NSIndexPath) {
      updateCount()
  }
  
  func updateCount(){
  
    let list = tableView.indexPathsForSelectedRows() as [NSIndexPath]
  
    println(list.count)
  </code></pre>
  
  <p>Everything works good until something is selected. But when there is no selected row, app crashes with "fatal error: unexpectedly found nil while unwrapping an Optional value".
  I think it is because selection is nil, but how to write this code with Optionals? I tried 
  many ways but app still crashes when I uncheck all selection. </p>