[gdm] slave: fix crasher in systemd integration

[Ray Strode <halfline src gnome org>]

commit 4c80969a0f8667d9a17ae44281cacb939e9f1a21
Author: Ray Strode <rstrode redhat com>
Date:   Thu Feb 9 13:27:11 2012 -0500

    slave: fix crasher in systemd integration
    
    sd_seat_get_sessions returns NULL instead of a one
    element array in the case there are no sessions
    associated with a seat.
    
    This commit guards against that problem.

 daemon/gdm-slave.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/daemon/gdm-slave.c b/daemon/gdm-slave.c
index 371b9bd..d864a3d 100644
--- a/daemon/gdm-slave.c
+++ b/daemon/gdm-slave.c
@@ -1336,6 +1336,11 @@ gdm_slave_get_primary_session_id_for_user_from_systemd (GdmSlave   *slave,
                 return NULL;
         }
 
+        if (sessions == NULL) {
+                g_debug ("GdmSlave: seat has no active sessions");
+                return NULL;
+        }
+
         for (i = 0; sessions[i] != NULL; i++) {
 
                 if (primary_ssid == NULL) {