Fix null pointer exceptions

Possible NPE issue that was seen in some bug reports where the playback state
or metadata was null after closing an app. Also added useful debug messages

Test: manual
Fixes: 129847573
Fixes: 129973823
Change-Id: I76d9f465072831dfe3457751a39e82bdd9b049b7
(cherry picked from commit 58e0ee0d)