Upstream gnulib patch to fix crash when gdm is in use. [bsc#1215361]

From 579f2d6f3d1d817c2f7e2c603c9a3ded63dcaa92 Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Fri, 15 Sep 2023 17:40:10 +0200
Subject: [PATCH] readutmp: Fix crash when gdm is in use.

Reported by Thorsten Kukuk <kukuk@suse.com> in
<https://lists.gnu.org/archive/html/bug-gnulib/2023-09/msg00093.html>.

* lib/readutmp.c (read_utmp_from_systemd): Don't use the value returned
by sd_session_get_display if it is NULL.
---
 lib/readutmp.c | 5 ++++-
 1 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/readutmp.c b/lib/readutmp.c
index ec09feb59b..d8213e7ad5 100644
--- a/lib/readutmp.c
+++ b/lib/readutmp.c
@@ -873,7 +873,10 @@ read_utmp_from_systemd (idx_t *n_entries, STRUCT_UTMP **utmp_buf, int options)
                           char *display;
                           if (sd_session_get_display (session, &display) < 0)
                             display = NULL;
-                          host = display;
+                          /* Workaround: gdm "forgets" to pass the display to
+                             systemd, thus display may be NULL here.  */
+                          if (display != NULL)
+                            host = display;
                         }
                     }
                   else
-- 
2.42.0