User switcher - Fix adding user as non-system user

The shade would stay expanded when adding a user as a non-system
user. Make sure the broadcast is sent as the current user in order to
be processed correctly.

Fixes: 219638055
Test: manual, as guest user attempt to add user multiple times
Change-Id: Ie293514fa4f8792616f5a0d7892c9010a8496ed0