sanity check for cell size update of tilemap that has no tiles to infer texture size from

nodes/TileMapObject.gd

@@ -32,6 +32,8 @@ func _enter_tree() -> void:
 func _update_cell_size(_p_old_cell_size: Vector2, p_new_cell_size: Vector2) -> void:
     # We're assuming that all tile textures are of same dimensions.
     # todo: Diagnose mismatch by walking over all textures?
+    if tile_set.get_tiles_ids().size() == 0:
+        return
     var tileset_texture_size := tile_set.tile_get_texture(0).get_size()
     scale = p_new_cell_size / tileset_texture_size
     cell_size = p_new_cell_size / scale