Prevent face auth from running again after a successful unlock when assistant is active.

Fixes: 264952680
Test: atest KeyguardUpdateMonitorTest
Test: manually,
  1. Enable face & fp unlock
  2. Enable AoD
  3. Enable assistant with voice trigger
  4. Hold phone in front of your face
  5. Go to AoD by pressing the power button
  6. Trigger assistant by saying "Ok Google"
  7. Assistant should open up on lockscreen.
  8. Say "setup an alarm"
  9. Face unlock should be triggered and device should be unlocked in the bg with keyguard being dismissed.
  10. Specify the time for the alarm verbally
  11. Once the alarm is set, tap the alarm on the assistant window
  12. Face unlock should not be triggered momentarily while assistant is dismissed.

Change-Id: Ie3eefc17bc81b2057f318ad53159f5c9b823721b