Actually use the argument in convert

conquest/regioner.py

@@ -549,6 +549,12 @@ class MapMaker(ConquestMap):
         return points
 
     async def convert_masks(self, regions):
+        if regions:
+            async for region in regions:
+                mask_path = self.masks_path() / f"{region}.png"
+                img: Image.Image = Image.open(mask_path).convert(MASK_MODE)
+                img.save(mask_path)
+        else:
             async for mask_path in AsyncIter(self.masks_path().iterdir()):
                 # Don't both checking if masks are in self.regions
                 img: Image.Image = Image.open(mask_path).convert(MASK_MODE)