In Ubuntu 19.10, we use GCC 9.2.1 and glib was failing to compile with
the following message:

  CC       libgio_2_0_la-gdbusauth.lo
gdbusauth.c: In function '_g_dbus_auth_run_server':
gdbusauth.c:1302:11: error: '%s' directive argument is null [-Werror=format-overflow=]
 1302 |           debug_print ("SERVER: WaitingForBegin, read '%s'", line);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors

So we apply this MR:
https://gitlab.gnome.org/GNOME/glib/-/merge_requests/626
corresponding to this commit:
https://gitlab.gnome.org/GNOME/glib/-/commit/2a9ddc630341789c629c17c17565f5a7a7db8a8e

"gdbus: Avoid printing null strings"