Two attempts at videoElementDestroyed after unsusbcribe

[d01010101]

Describe the bug This is just my guess. Possibly related to https://github.com/OpenVidu/openvidu/issues/129.

Occasionally, after unsubscribe, OpenVidu correctly removes its video element, emits videoElementDestroyed and then attempts to do it again. The video element is no more there, so an error is produced.

Console:

OpenViduLogger.ts:31 Event 'videoElementDestroyed' triggered by 'Subscriber' 
VideoElementEvent {hasBeenPrevented: false, cancelable: false, target: Subscriber, type: "videoElementDestroyed", element: video#remote-video-str_CAM_TuEE_con_NZFNg3QpWU}
VIDEO ELEMENT DESTROYED HANDLER CALLED
OpenViduLogger.ts:31 Unsubscribed correctly from con_NZFNg3QpWU
OpenViduLogger.ts:31 Inbound WebRTCPeer from 'Stream' with id [str_CAM_TuEE_con_NZFNg3QpWU] is now closed
OpenViduLogger.ts:31 Remote MediaStream from 'Stream' with id [str_CAM_TuEE_con_NZFNg3QpWU] is now disposed
OpenViduLogger.ts:31 Event 'streamDestroyed' triggered by 'Session' 
StreamEvent {hasBeenPrevented: false, cancelable: true, target: Session, type: "streamDestroyed", stream: Stream, …}
STREAM DESTROYED HANDLER CALLED
OpenViduLogger.ts:31 Calling default behavior upon 'streamDestroyed' event dispatched by 'Session'
OpenViduLogger.ts:31 Inbound WebRTCPeer from 'Stream' with id [str_CAM_TuEE_con_NZFNg3QpWU] is now closed
OpenViduLogger.ts:31 Remote MediaStream from 'Stream' with id [str_CAM_TuEE_con_NZFNg3QpWU] is now disposed
OpenViduLogger.ts:42 TypeError: Cannot read property 'removeChild' of null
    at StreamManager.ts:428
    at Array.forEach (<anonymous>)
    at Subscriber.StreamManager.removeAllVideos (StreamManager.ts:420)
    at StreamEvent.callDefaultBehavior (StreamEvent.ts:97)
    at Session.ts:734

The error happens in the first line of

streamManagerVideo.video.parentNode!.removeChild(streamManagerVideo.video);
this.ee.emitEvent('videoElementDestroyed', [new VideoElementEvent(streamManagerVideo.video, this, 'videoElementDestroyed')]);

Expected behavior A single attempt at destroying the video element. Or, if do something wrong, reporting it instead of calling twice the same videoElementDestroyed.

Wrong current behavior First attempt removes the component, the second one produces an error about a missing component.