AudioPlayerStateMonitor: fix NPE

Use PLAYER_STATE_UNKNOWN for state passed to
sendAudioPlayerStateChangedMessageLocked() when prevState
is null in dispatchPlaybackConfigChange()

Bug: 68748062
Test: receive a call and check ringtone
Test: passed media cts
Change-Id: I9d4c84dc1d79a72afd06d044d00f682b70c86255
1 file changed