Refresh the now playing ID map when the now playing list changes

The Now Playing List ID's could be invalid if the now playing list
changes but there is not track change, like when adding a song to the
queue on the device.

Bug: 68812037
Test: Run host native test net_test_avrcp
Change-Id: I3c2c11aa87b64241f378819c38ae5cc21ffdb5ac