title: How could tableView:commitEditingStyle:forRowAtIndexPath: be called with a nil indexPath?
body: <p>I finally tracked down a weird crash. It is caused by <code>tableView:commitEditingStyle:forRowAtIndexPath:</code> being called with a <code>nil</code> indexPath. But how can it be?</p>
  
  <pre><code>- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
      if (editingStyle == UITableViewCellEditingStyleDelete) {
          // DEBUG
          if (indexPath == nil) {
              NSLog(@"Deleting row at nil indexPath in %@", self);
          }
          [self deleteItemAtIndexPath:indexPath fromTableView:tableView];
      }
  }
  </code></pre>
  
  <p>Here is the stack trace:</p>
  
  <pre><code>6    XXX     -[ListViewController tableView:commitEditingStyle:forRowAtIndexPath:] (ListViewController.m:427)
  7    UIKit   -[UITableView(UITableViewInternal) animateDeletionOfRowWithCell:] + 85
  8    UIKit   -[UIApplication sendAction:to:from:forEvent:] + 73
  9    UIKit   -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 31
  10   UIKit   -[UIControl sendAction:to:forEvent:] + 45
  11   UIKit   -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 503
  12   UIKit   -[UIApplication sendAction:to:from:forEvent:] + 73
  13   UIKit   -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 31
  14   UIKit   -[UIControl sendAction:to:forEvent:] + 45
  15   UIKit   -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 503
  16   UIKit   -[UIControl touchesEnded:withEvent:] + 489
  17   UIKit   -[UIWindow _sendTouchesForEvent:] + 525
  18   UIKit   -[UIApplication sendEvent:] + 381
  19   UIKit   _UIApplicationHandleEvent + 6155
  20   GraphicsServices    _PurpleEventCallback + 591
  21   CoreFoundation  __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
  22   CoreFoundation  __CFRunLoopDoSources0 + 213
  23   CoreFoundation  __CFRunLoopRun + 647
  24   CoreFoundation  CFRunLoopRunSpecific + 357
  25   CoreFoundation  CFRunLoopRunInMode + 105
  26   GraphicsServices    GSEventRunModal + 75
  27   UIKit   UIApplicationMain + 1121
  28   XXX     main (main.m:16)
  29   XXX     start + 40
  </code></pre>