Crash more quickly if (offline) console is resized too small

Crash more quickly if (offline) console is resized too small

If `winner` is not valid here, then some of the following coordinate
assignments will also be invalid and lead to somewhat unpredictable
crashes later (because the `valid` bool is set basically if the
coordinate setup aborts in the middle). This standardizes the crashes.

What would be much, much better is if the display just blanked with a
message saying "your term is too small" until the player resized again,
without crashing.