Fix boot loop when upgrading direclty from L to N

A second attempt to fix the upgrade problem due to SID == 0
in the above upgrade path. The previous fix contains a bug
where it would cause future attempts to unify work challenge
to silently fail, and crash SystemUi when unlocking.

This fix adds a check for non-zero SID before doing the initial work
profile unification (which caused the upgrade crash when SID == 0).
This means the initial work profile unification would only happen when
the user has unlocked the lockscreen and SID is generated.

Bug: 32490092
Bug: 33050562
Change-Id: Ib28951b2ec26b4f091df7763d9902f55616fcb5c