======================
    if (!g_key_file_load_from_file (config, CFG_KEY_FILE,
                                    G_KEY_FILE_NONE, &err))
    {
        g_error (_("Couldn't load configurations file!"));
        exit (EXIT_FAILURE);
    }
======================
normally this code will read & parse the key file. but if the file is empty then it will return an error.

So I must write the workaround:
======================
    int fd = open (CFG_KEY_FILE, O_RDWR | O_CREAT);
    if (!fd)
    {
        g_error (_("Couldn't create key file: %s"), strerror (errno));
        exit (EXIT_FAILURE);
    }
    struct stat buf;
    fstat (fd, &buf);
    if (buf.st_size == 0)
    {
        lseek (fd, 0L, SEEK_SET);
        write (fd, "#\n", 2);
    }
    close (fd);
======================
But I think, the function, g_key_file_load_from_file() should not return an error if the file is empty.