Handle async behavior with CE in UsageStats.

With the migration of usage stats data to CE, it's possible for a user
unlock event to be handled after the user has been removed. To prevent
exceptions from being thrown when the user is stopped or removed, when
an exception is thrown, check if the user is unlocked, only then throw
the exception.

Bug: 141307758
Test: atest CtsDevicePolicyManagerTestCases
Change-Id: I70fdb56dd6e87dc911c400554a4b5760785b87a4