ref: 9e2e0692ed087dbe0d5f4abbddf3aebd6a11b30e
parent: 5cc9bfb811854b66c4a570e8100b8a1aad037f0e
author: Ben Harris <bjh21@bjh21.me.uk>
date: Mon Jan 9 19:22:57 EST 2023
Also check for tiny grids in Mines A zero-size grid isn't acceptable even if someone has generated it for us.