You could try replacing
"g_spawn_command_line_sync ("xflock4", NULL, NULL, exit_status, error);"
by
"g_spawn_command_line_sync ("xflock4", NULL, NULL, exit_status, NULL);"
(In git in calls of g_spawn_command_line_async NULL is used for the error parameter (in xfce-sreensaver.c). Error variable might have some additional information about the error, though.
You could try replacing command_ line_sync ("xflock4", NULL, NULL, exit_status, error);" command_ line_sync ("xflock4", NULL, NULL, exit_status, NULL);"
"g_spawn_
by
"g_spawn_
(In git in calls of g_spawn_ command_ line_async NULL is used for the error parameter (in xfce-sreensaver.c). Error variable might have some additional information about the error, though.