If we're running in legacy mode where VT1 is not necessarily a login
screen, then we can end up in a situation where logging out leaves us
sitting on the wrong vt.

1) log in to user 1 on vt 1
2) switch user to login screen on vt 2 and log in as user 2 on vt 2
3) switch user to login screen on  vt 3 and unlock user 1 back on vt 1
4) log out of user 1 on vt 1
5) now sitting at blank vt 1

This commit makes sure in that case we jump to a login screen

https://bugzilla.gnome.org/show_bug.cgi?id=780914