Make scheduler robust to duplicate finish calls

Mis-implemented clients may invoke onClientFinished more than once.
The scheduler should be robust to this, and assume that the first
onClientFinished is the one that matters.

Test: atest BiometricSchedulerTest

Bug: 161325267
Change-Id: Ifc64fd4732d2abe03738dda270feeb29bb818bcf
2 files changed