don't add duplicate tiles

src/lib.rs

@@ -57,20 +57,23 @@ pub fn add_tiles(game_data: String, image: String, prefix: String) -> String {
                 }
             }
 
-            game.add_tile(Tile {
+            let tile = Tile {
                 /// "0" will get overwritten to a new, safe tile ID
                 id: "0".to_string(),
                 name: tile_name(&prefix, &tile_index),
                 wall: None,
                 animation_frames: vec![Image { pixels }],
                 colour_id: None
-            });
+            };
+
+            if !game.tiles.contains(&tile) {
+                game.add_tile(tile);
 
                 tile_index += 1;
             }
         }
+    }
 
-    game.dedupe_tiles();
     game.to_string()
 }