message: Checked scenes count instaed of crumb
  Consistent with the java check
diff: {
  [super didSetProps:changedProps];
  NSInteger eventLag = _nativeEventCount - _mostRecentEventCount;
  - NSInteger crumb = [self.keys count] - 1;
  - if (eventLag != 0 || crumb == -1)
  + if (eventLag != 0 || _scenes.count == 0)
  return;
  + NSInteger crumb = [self.keys count] - 1;
  NSInteger currentCrumb = [_navigationController.viewControllers count] - 1;
  if (crumb < currentCrumb) {
  [_navigationController popToViewController:_navigationController.viewControllers[crumb] animated:true];
  