Fix crash when decrementing data usage request

When unregistering, if the caller process is dead. The system
can unregsiter for the caller. But the request decrement should
be counted onto the caller uid instead of system uid.

Test: NetworkStatsObserversTest#testUnregister_knownRequest_invalidUid_doesNotUnregister
Bug: 233580307
Change-Id: I85aee8f395739929bc7086883ace81ac1ecd0730
Merged-In: I85aee8f395739929bc7086883ace81ac1ecd0730
  (pure cherry-picked from ag/18579047)
2 files changed