commit c0188a70 added some complex code for starting
the login screen when the user switches to the initial
VT if nothing is running on that VT.

The problem is, we get a VT change event on that VT as
part of the start up process.

This leads to an additional greeter getting started.

This commit adds a check to side step the new code during
startup.

Closes: GNOME/gdm#409