fix(breakout-rooms) fix not waiting to leave the room

We need to wait for it before we start joining.

react/features/breakout-rooms/actions.js

             dispatch(setVideoMuted(video.muted));
         } else {
             try {
-                APP.conference.leaveRoom(false /* doDisconnect */);
+                await APP.conference.leaveRoom(false /* doDisconnect */);
             } catch (error) {
                 logger.warn('APP.conference.leaveRoom() rejected with:', error);