ksmserver: reject new XSMP clients earlier in the shutdown path
Reason for the change
When we are ending the session, a new client connecting and trying to register causes things to get confused and long delays to happen.
See also https://bugzilla.gnome.org/show_bug.cgi?id=688209
Test plan
Ask an affected user to test the patch
Screenshots or screen recordings
Bugs fixed
BUG: 488853 FIXED-IN: 6.1.5