Prevent SystemUISecondaryUserService from screwing up SystemUI.

SystemUISecondaryUserService, when started for the primary user and
when started before other services causes the systemui process to
fail to initialize itself properly.

This CL adds safety checks that prevent that from happening.

Flag: NA
Fixes: 322102041
Test: built and run. Switched users.
Change-Id: I9bbc21b83b507b363b7ec3dde126e374f70ef4ce