FIX: rdwr_str must not return NULL plainstring

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6357 8aca7d54-2c30-db11-9de9-000461428c89
CODE: do not call set_focus from within action_triggered, it may not
have any effect
FIX: properly release focus in depot window after e.g. creating line


git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6358 8aca7d54-2c30-db11-9de9-000461428c89
Another call of set_focus removed

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6360 8aca7d54-2c30-db11-9de9-000461428c89