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.

Ignore-AOSP-First: Urgent fix
Test: NetworkStatsObserversTest#testUnregister_knownRequest_invalidUid_doesNotUnregister
Bug: 233580307
Change-Id: I85aee8f395739929bc7086883ace81ac1ecd0730
2 files changed