This is a follow up to bug 6956.
When shutting down apps in an appgroup, its possible to crash the Xserver.
I don't know if this is dependent on a busy host or not.
A for-loop in CheckConnections() uses a local copy of the select file descriptor
list, which can change when an appgroup is shutting down.
The attached patch checks for a valid ConnectionTranslation entry prior
to calling CloseDownClient() with a null value.
Created attachment 6550 [details] [review]
committed to master and server 1.2 branch, thanks a bunch