From: Marc-André Lureau <marcandre.lureau@redhat.com>

When closing the QEMU Gtk display window, it can occasionaly warn:
qemu-system-x86_64: Gtk: gtk_clipboard_set_with_data: assertion 'targets != NULL' failed

#3  0x00007ffff4f02f22 in gtk_clipboard_set_with_data (clipboard=<optimized out>, targets=<optimized out>, n_targets=<optimized out>, get_func=<optimized out>, clear_func=<optimized out>, user_data=<optimized out>) at /usr/src/debug/gtk3-3.24.30-4.fc35.x86_64/gtk/gtkclipboard.c:672
#4  0x00007ffff552cd75 in gd_clipboard_update_info (gd=0x5555579a9e00, info=0x555557ba4b50) at ../ui/gtk-clipboard.c:98
#5  0x00007ffff552ce00 in gd_clipboard_notify (notifier=0x5555579aaba8, data=0x7fffffffd720) at ../ui/gtk-clipboard.c:128
#6  0x000055555603e0ff in notifier_list_notify (list=0x555556657470 <clipboard_notifiers>, data=0x7fffffffd720) at ../util/notify.c:39
#7  0x000055555594e8e0 in qemu_clipboard_update (info=0x555557ba4b50) at ../ui/clipboard.c:54
#8  0x000055555594e840 in qemu_clipboard_peer_release (peer=0x55555684a5b0, selection=QEMU_CLIPBOARD_SELECTION_PRIMARY) at ../ui/clipboard.c:40
#9  0x000055555594e786 in qemu_clipboard_peer_unregister (peer=0x55555684a5b0) at ../ui/clipboard.c:19
#10 0x000055555595f044 in vdagent_disconnect (vd=0x55555684a400) at ../ui/vdagent.c:852
#11 0x000055555595f262 in vdagent_chr_fini (obj=0x55555684a400) at ../ui/vdagent.c:908

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 ui/gtk-clipboard.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/ui/gtk-clipboard.c b/ui/gtk-clipboard.c
index 35b7a2c22838..0ed630cf9b68 100644
--- a/ui/gtk-clipboard.c
+++ b/ui/gtk-clipboard.c
@@ -84,7 +84,7 @@ static void gd_clipboard_notify(Notifier *notifier, void *data)
     if (info != qemu_clipboard_info(s)) {
         gd->cbpending[s] = 0;
         if (!self_update) {
-            GtkTargetList *list;
+            g_autoptr(GtkTargetList) list = NULL;
             GtkTargetEntry *targets;
             gint n_targets;
 
@@ -95,15 +95,16 @@ static void gd_clipboard_notify(Notifier *notifier, void *data)
             targets = gtk_target_table_new_from_list(list, &n_targets);
 
             gtk_clipboard_clear(gd->gtkcb[s]);
-            gd->cbowner[s] = true;
-            gtk_clipboard_set_with_data(gd->gtkcb[s],
-                                        targets, n_targets,
-                                        gd_clipboard_get_data,
-                                        gd_clipboard_clear,
-                                        gd);
-
-            gtk_target_table_free(targets, n_targets);
-            gtk_target_list_unref(list);
+            if (targets) {
+                gd->cbowner[s] = true;
+                gtk_clipboard_set_with_data(gd->gtkcb[s],
+                                            targets, n_targets,
+                                            gd_clipboard_get_data,
+                                            gd_clipboard_clear,
+                                            gd);
+
+                gtk_target_table_free(targets, n_targets);
+            }
         }
         return;
     }
-- 
2.34.1.8.g35151cf07204