Fixed error with edit field discovered by An_dz

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6976 8aca7d54-2c30-db11-9de9-000461428c89
Another small error when dragging bridges

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6977 8aca7d54-2c30-db11-9de9-000461428c89