Only empty tiles should be changed to walls, obviously...

squirrelbattle/mapgeneration/randomwalk.py

@@ -107,6 +107,7 @@ class Generator:
         # post-processing: add walls
         for x in range(width):
             for y in range(height):
+                if grid[y][x] == Tile.EMPTY:
                     c = sum([1 if grid[j][i] == Tile.FLOOR else 0 for j, i in result.large_neighbourhood(y, x)])
                     if c == 4 and self.params["no_lone_walls"]:
                         result.tiles[y][x] = Tile.FLOOR