Make ChooseLockGeneric read the userId extra from the activitie's extras if there's no arguments

Some invocations of ChooseLockGeneric are done with arguments, but
when invoking it from FingerprintEnrollIntroduction we add the extra
to the activity intent so we need to support both.

Bug: 26901625
Change-Id: Iaabad18bf17160578f6b6d807dc6acfead1ba419