Attachments marked as shutdown may still be running (before they reach the rescheduling point), so they should not be accounted as already gone. This should also fix CORE-4236: Database shutdown is reported as successfully completed before all active connections are in fact interrupted.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58780 65644016-39b1-43b1-bf79-96bc8fe82c15