Fix clock fading in incorrectly

In some cases, when going from AOD->LOCKSCREEN, the isDreaming value
may still be true after the transition is started, producing a visual
flicker as the lockscreen comes up.

Don't allow DREAMING to interrupt AOD->LOCKSCREEN

Fixes: 271919264
Test: atest KeyguardTransitionScenariosTest
Test: manual test transitions for both T & U devices
Change-Id: If1028d4a98b52133790a0d97aee798c8d659ab6b