Closing all application windows and retaining access to the application menu
is only possible on MacOSX. The DispatchProvider used for the update check
seems to depend on having an active application window. Maybe it is possible
to get the update check working without it but this patch doesn't attempt
that, it prevent further escalation such as crashes.

Fixed by: Herbert Duerr
Debugged by: Oliver-Rainer Wittmann, Herbert Duerr
Found by: Frantisek Erben