[Minor] Check type of map more strictly

src/lua/lua_map.c

@@ -384,9 +384,12 @@ lua_config_add_map (lua_State *L)
 
 		g_assert (map_obj != NULL);
 
-		if (type == NULL) {
+		if (type == NULL && cbidx != -1) {
 			type = "callback";
 		}
+		else if (type == NULL) {
+			return luaL_error (L, "invalid map type");
+		}
 
 		if (strcmp (type, "callback") == 0) {
 			map = rspamd_mempool_alloc0 (cfg->cfg_pool, sizeof (*map));