Fix warning

src/api/system.c

@@ -524,6 +524,7 @@ static int f_on_file_saved(lua_State *L) {
   const char *filename = luaL_checkstring(L, 1);
   if (g_liteOnFileSavedCallback)
     g_liteOnFileSavedCallback(filename);
+  return 1;
 }
 
 static int f_get_clipboard(lua_State *L) {