Mitigate IPC calls from MultiUserSwitcher

Reduce the calls to UserManager#hasUserRestriction when checking if the
switcher should be shown by reordering the conditions. In most cases,
the switcher is disabled (from settings) and it will short circuit.

TODO: actually remove the call from main thread

Test: manual, when device does not have multiple users, there are no
calls to UserManager
Bug: 138640355
Bug: 138661450

Change-Id: I35905d4d8a7194866f55009b86dff0a2a4214e1a