[2.0.77] Allow adding rails on other surfaces in LuaSchedule::add_record

[hgschmie]

When trying to add a new schedule record to a LuaSchedule for a train, if the AddRecordData refers to a rail, the rail must be on the same surface as the train.

Now, this makes sense for the base game, but it makes scheduling routes that cross surfaces (e.g. LTN + Space Exploration) difficult. While it is possible to schedule actual train stops by name (they just turn red), adding the temp stops that direct a train to a specific stop only works if the train is on the same surface as the rail.

Is it possible to remove this restriction? There seems to be no actual reason within the engine (having stops on other surfaces works fine).