FIX display of walls in sliced underground view

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6807 8aca7d54-2c30-db11-9de9-000461428c89
CODE: reduce scope of variable

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6808 8aca7d54-2c30-db11-9de9-000461428c89
FIX: world-view element to work properly with sliced underground mode

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6809 8aca7d54-2c30-db11-9de9-000461428c89