Fix flicker in lockscreen if music controls are disabled.

Pretend no music is playing if music controls are disabled, as otherwise
KeyguardHostView gets confused as there's a mismatch between the result
of isMusicPlaying() and the onListenerAttached() / onListenerDetached()
callbacks.

Change-Id: Ic3bd2c6f143ce8b67c80abb408a4ff463ebae53d
JIRA:CYAN-1935