Send UID 0 for track changed if there is no media ID

Some carkits need the track changed UID to change even though we
explicitly report that UID's are refreshed on any now playing list
change. UID 0 is special since it represents that the song has changed
and forces an update.

Bug: 72824896
Test: Tested with Audi carkit where Spotify wasn't updating past the
first song previously.

Change-Id: I033f9a2f96acfde25922d6912a4927b95fb89596