[bug: latest release] Line with no name ends with a crash

[Borgoth]

Easily repeatable.
Make a line. Put a train on that line. Delete the name of the line (i.e. leaving the name empty). Open train schedule. Try to change the train to a different line. Crash.

PS. Don't do like me and forget to save for 8 hours.  :'(

[Dwachs]

should be fixed in rev 2599