Fix crash after confirmLock

Stop everything in generateChallenge() on "Face and Fingerprint Unlock"
page if activity is null or finishing

Also fix ignored test cases in CombinedBiometricProfileSettingsTest

Bug: 292125215
Test: RunSettingsRoboTests ROBOTEST_FILTER=CombinedBiometricProfileSettingsTest
Change-Id: I7a272e813bfddd5d066417a74cbd63d22f511000