Fix for SF bug #
1086664: Repeatable crash closing window.
Closing a window while a modal dialog is up, triggered from a find or
replace dialog button action routine, is virtually impossible.
We can prevent illegal accesses to destroyed windows (which is the reason
for the crash), but we cannot avoid that Motif accesses structures that
get destroyed in the process.
Therefore, it is now no longer possible to close a window via the window
manager during the execution of a search dialog button action routine in
that window.