resource: fix unused variable warning

src/resource/resource_manager.cpp

@@ -141,8 +141,8 @@ const void *ResourceManager::get(StringId64 type, StringId64 name)
 	const ResourcePair id = { type, name };
 
 	const ResourceId res_id = resource_id(type, name);
-
 	CE_ASSERT(can_get(type, name), "Resource not loaded: " RESOURCE_ID_FMT, res_id._id);
+	CE_UNUSED(res_id);
 
 	if (_autoload && !hash_map::has(_rm, id)) {
 		load(type, name);