FIX crash when opening depot and no lines available

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6771 8aca7d54-2c30-db11-9de9-000461428c89
FIX problems with selecting lines in depot window

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6772 8aca7d54-2c30-db11-9de9-000461428c89