Keep the last track piece clear

KRS had the following problem: If you put an engine on the last piece of a terminal track, you hit a bug in the code which does nothing but issuing a complaint in LogMate that it "cannot back propagate". However, this consumed time and if you happened to trigger this for a lot of track pieces, you ran into serious trouble.

Will not happen, you say, but you forgot about turntables. They have a large number of short tracks leading from them, typically just single straight pieces, and many of them hold an engine. Turntables had a reputation for creating weird problems. Adding a (really) short piece of track at each track end cured the problem, as far as I remember the feedback from people.

Now in RW, this error seems to have mutated to a fatal scenario loading error, where the game talks about "Invalid Constist Error". I looks like RSC wanted to rule out the above bug by forbidding the placement of trains on the critical track piece. But this last piece can be really long, if the route builder does not know about the issue.

The workaround for the time being is that all route builders split and reweld the last piece of track near the buffers, or add a foot of track there. That way, no one can place anything in the critical place and it does not matter if the bug currently leads to slow game performance, crashes, or refusal to load a scenario.