VideoPlayer: fix audio playback when leaving pip

When you open pip with play in background, when you quit pip, in the onStop, it will switch to audio.

If you check if system Pip is running you can stop that, but it will stop playback from running with the screen off, so check for screen off also.

This means that isInPiPMode will stay true, even though PiP has been killed a while ago, audio playback in background is still running.