BHV-12306: VideoPlayer does not unload video

### Issue
Missing initialization on sources

### Fix
Add sources set to null on unload.

DCO-1.1-Signed-Off-By: Kunmyon Choi kunmyon.choi@lge.com
Merge pull request #1506 from enyojs/BHV-12306-kunmyonchoi-new

BHV-12306: VideoPlayer does not unload video