Check for null in addition to instanceof Face

We only send a Face object if the client holds the MANAGE_BIOMETRIC
permission. Otherwise we send null. Fixes the issue where clients that
don't have the MANAGE_BIOMETRIC permission don't receive
onAuthenticationSucceeded callback.

Test: Builds
Change-Id: If1742570ebe914d0ba7da17e60655fed3c9a4b39