Cleanly handle unknown response codes in setLockCredentialInternal()

Instead of throwing an exception when getting an unknown
VerifyCredentialResponse code, just treat RESPONSE_ERROR and unknown
codes the same way.  This is needed to prevent the exception case from
being reached when RESPONSE_ERROR is split up.

A later CL could introduce different behavior for different response
codes, such as logging different messages.  For now I'd simply like to
make this call site consistent with all other non-test code, which does
not differentiate between RESPONSE_ERROR and unknown errors.

Test: atest FrameworksServicesTests:com.android.server.locksettings
Bug: 395976735
Flag: EXEMPT only changes behavior in case that isn't reachable yet
Change-Id: I55c7f841fa15027209de4ae9f46f2cd725e167d0