FIX crash when there is waypoint after depot

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6366 8aca7d54-2c30-db11-9de9-000461428c89
FIX aircraft landing height adjustment: do not crash into mountain, do not fall from sky if runway is too low

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6367 8aca7d54-2c30-db11-9de9-000461428c89
Praparing for landing again not with full speed

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6368 8aca7d54-2c30-db11-9de9-000461428c89