Mark mAutomaticBrightnessController @Nullable.

Check that AutomaticBrightnessController is not null before calling update() and resetShortTermModel().

Bug: 203737431
Test: manual: flashed build with automaticBrightnessController set to null and verified that no NPE is thrown.
Change-Id: Ie709d4bc7e6166eeb7e936bea79162f468c713f4
(cherry picked from commit 4d9cb42e217fd2c105c8a141ec849968584e2878)
1 file changed