iOS 14 popToRoot的时候，tabbar不显示的问题

之前是这样写的：

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated{
    if (self.viewControllers.count) {
        viewController.hidesBottomBarWhenPushed = YES;
    }
    [super pushViewController:viewController animated:animated];
}

改成这样写：

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated {
    if (self.viewControllers.count > 0) {
        // 当前导航栏, 只有第一个viewController push的时候设置隐藏
        if (self.viewControllers.count == 1) {
            viewController.hidesBottomBarWhenPushed = YES;
        }
    } else {
        viewController.hidesBottomBarWhenPushed = NO;
    }
    [super pushViewController:viewController animated:animated];
}