don't try to get tiles with ID of zero; test this

src/game.rs

@@ -230,7 +230,7 @@ impl Game {
         if ! avatar_exists {
             return Err(NotFound::Avatar);
         }
-        
+
         Ok(
             Game {
                 name,
@@ -318,6 +318,12 @@ impl Game {
         let mut tile_ids = room.unwrap().tiles.clone();
         tile_ids.sort();
         tile_ids.dedup();
+        // remove 0 as this isn't a real tile
+        let zero_index  = tile_ids.iter()
+            .position(|i| i == &"0".to_string());
+        if zero_index.is_some() {
+            tile_ids.remove(zero_index.unwrap());
+        }
         // remove Ok once this function returns a result
         Ok(self.get_tiles_by_ids(tile_ids))
     }
@@ -679,4 +685,12 @@ mod test {
         game.version = Some(Version { major: 5, minor: 0 });
         assert!(game.to_string().contains("# BITSY VERSION 5.0"))
     }
+
+    #[test]
+    fn test_get_tiles_for_room() {
+        assert_eq!(
+            crate::mock::game_default().get_tiles_for_room("0".to_string()).unwrap(),
+            vec![&crate::mock::tile_default()]
+        )
+    }
 }