Freeciv

Split from #2366 reported by Eelis Vuokko

When one attempts to create an overlong goto route in the client, the result is usually some kind of crash. It varies how and where it crashes, but at least once I got
1: in make_path_orders() [../../src/client/goto.c::1416]: assertion '*length < MAX_LEN_ROUTE' failed.

Later it also said:
1: Trying to put 1266 into 8 bits; it will result 242 at receiving side.

For now, I treat this latter error as a consequence of the first one (likely trying to send uninitialized steps over the MAX_LEN_ROUTE), and not a separate issue.

I had fix for #2366 applied.