Fixed an issue where the media notification wouldn't have contrast

Because we were relying on the output to go in the right direction
already, this could be wrong. We're now only following the given
lightness direction if it is even possible to satisfy contrast.

Test: runtest -x core/tests/coretests/src/android/app/NotificationTest.java
Change-Id: I06d934a6b5c328ebbf0cf707030b0d707ccb5ab4
Fixes: 38182819