Fix: Don't allow towns to terraform certain floodable tiles #8492
Prevent rare occurrences of roads and houses being flooded, resulting in disconnected towns.
Motivation / Problem
Void tiles are a problem. Terraform command ignores them. If the town terraforms one of the tiles at the edges of the map, there's no checking happening for the void tiles, and it may result in a flood coming in the direction of the void tile.
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.