fix videoplayer crash in release mode

[minggo]

崩溃的调用顺序是这样的：

VideoPlayer::~VideoPlayer() -> UIVideoViewWrapperIos.dealloc() -> UIVideoViewWrapperIos.clean() -> UIVideoViewWrapperIos.stop() -> VideoPlayer::onPlayEvent()

也就是说 VideoPlayer 的析构函数会调用到事件监听的回调函数，但这时的事件监听者可能已经释放了，所以不在析构时去调用监听函数。

[cocos-robot]

@minggo, v2.1.4-release branch will be deleted, so we edited the base branch to v2.2.1-release, or this PR will be killed by GitHub.
Please review the commits history to ensure that the PR does not polluted by unneeded commits from your origin branch.
If you need to merge to other branch, you can first click the Edit button on the right side of the PR title, then switch the base branch.
If necessary, welcome to resubmit a new PR. Thanks!