message: Checked if navigation controller before return visiblevc
diff: - (UIViewController *)navigation_childViewControllerForStatusBarStyle
  {
  - return ((UINavigationController *) [[self childViewControllers] lastObject]).visibleViewController;
  + UIViewController *viewController = [[self childViewControllers] lastObject];
  + return [viewController isKindOfClass:[UINavigationController class]] ? ((UINavigationController *) viewController).visibleViewController : nil;
  }
  - (UIViewController *)navigation_childViewControllerForStatusBarHidden
  {
  - return ((UINavigationController *) [[self childViewControllers] lastObject]).visibleViewController;
  + UIViewController *viewController = [[self childViewControllers] lastObject];
  + return [viewController isKindOfClass:[UINavigationController class]] ? ((UINavigationController *) viewController).visibleViewController : nil;
  }
  + (void)load
  