fw/b: Resolve black forced lights with notifications channels

 * The initial fix for blue lights upon 0x00000000 color selection
   in the settings by change Ia03f898c1b6cd0f77af8bb155139b587664f47af
   (fw/b lights: Allow black notification color) no longer works
   because the notification now uses channels, hence bypassing
   the "mPreChannelsNotification" checks used in this condition

 * Instead, validate the lights is forced on and black
   before calling the Lineage lights colors calculation

Change-Id: Iafac2c51878d84afd980b378b1c53f6c31073d2c