Fix a memleak before assertion in l_get_mod_storage

src/script/lua_api/l_storage.cpp

@@ -37,6 +37,7 @@ int ModApiStorage::l_get_mod_storage(lua_State *L)
		store->load(gamedef->getModStoragePath());
		gamedef->registerModStorage(store);
	} else {
		delete store;
		assert(false); // this should not happen
	}