FIX crash when window could not restored during reloading

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6371 8aca7d54-2c30-db11-9de9-000461428c89
More reliable retrieving of convois

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6372 8aca7d54-2c30-db11-9de9-000461428c89