FIX segfaults on pak selection related to background_dirty()

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6452 8aca7d54-2c30-db11-9de9-000461428c89
corrected spaces->tabs on my last update on grund.cc

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6453 8aca7d54-2c30-db11-9de9-000461428c89