Check if player is actually playing before calling stop(for_replacement=True)
in MpvMediaPlayer.play(). When the player was already idle,
stop(for_replacement=True) would set _suppress_end_event=True with no
end-file event to consume it. The next track's end-file callback would
then be incorrectly suppressed, breaking the timer loop.
- Import PlayerState to check player state
- Only call stop(for_replacement=True) when player is not IDLE