Added user exist check in SystemService post-completed user event

Added an additional check to verify if the userId exists,
In case userId does not exist the method will return
without sending any post-completed user events.

Test: atest UserControllerTest
Test: atest SystemServiceManagerTest

Bug: 242226766
Change-Id: If5bb7420a91a60a7907aede4e140f47ea0ab10d6
2 files changed