Ensure secondary sysui service starts

If a system boots and switches into a secondary user prior to SystemUI
initializing, the ACTION_USER_SWITCHED intent will not be received and
the secondary service will never be started. By checking the current
user on init, it is ensured that we do not miss this case.

Bug: 286338771
Test: manual, atest com.android.systemui.user

Change-Id: Ic3110213db96c29f7943604c451aec1ac9b254fc