NotificationLight: Fix forced close on non voice capable devices

Change-Id: Ib2c1e7d22414cff3ce06936a75d9de342b32320f
Fix button brightness preview.

Change-Id: I2b0933062d443855114088e1bb4c09c68a83a0e5
Merge "NotificationLight: Fix forced close on non voice capable devices" into cm-10.2