Cancel the shutdowner at the end of didShutdown in case shutting down emptied the room and caused it to schedule.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@5522 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/crowd/server/PlaceManager.java

@@ -538,6 +538,9 @@ public class PlaceManager
                 delegate.didShutdown();
             }
         });
+
+        // if shutting down emptied the place and scheduled the shutdowner, clear that out
+        cancelShutdowner();
     }
 
     /**