errorcheck for 0 valid csv lines

[yakra]

Came across this while using valgrind to troubleshoot something unrelated.

If there are 0 valid .csv lines, siteupdate goes on to allocate a block of 0 B for the routes and/or con_routes arrays.
Which is implementation-defined behavior. Wacky antics may ensue.

Sure, I could just skip the allocation, create a HighwaySystem object with 0 routes, and move on without complaining. But ISTM that's just bad juju. Seems that's just asking for a division by 0 error somewhere down the line. What if a 0-route system is in systems.csv as active or preview?

Making this an ErrorList item is The Right Thing To Do.

Nota Bene:

This flags both inddl.csv & inddl_con.csv.
The quickest & easiest solution is to comment inddl out in systems.csv.