Fix crash from UserNameViewController.removeAll()

The UserNamveViewController was calling removeListener() before the
listener had been registered. Added a boolean mRegistered to check if
the listener has been registered before removing it and added a test
that calls removeAll() before a listener is registered.

Bug: 168065924
Test: atest UserNameViewControllerTest
Change-Id: If24374e51a61c943142ba3a8794aca548dd241cc