FIX stupid error

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6941 8aca7d54-2c30-db11-9de9-000461428c89
FIX: only server is allowed to announce to listing server

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6942 8aca7d54-2c30-db11-9de9-000461428c89