[gtk/clipboard-test] Fix the clipboard test under X11

[Matthias Clasen <matthiasc src gnome org>]

commit 6482954c6e4a3701a3847ee879bc126bd147d89e
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Apr 30 08:02:35 2021 -0400

    Fix the clipboard test under X11
    
    We don't have a signal handler to worry about here.

 testsuite/gdk/clipboard-client.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/testsuite/gdk/clipboard-client.c b/testsuite/gdk/clipboard-client.c
index 346bac2d7c..c7ec502111 100644
--- a/testsuite/gdk/clipboard-client.c
+++ b/testsuite/gdk/clipboard-client.c
@@ -189,7 +189,8 @@ do_it (GObject    *object,
 {
   GdkClipboard *clipboard;
 
-  g_signal_handler_disconnect (object, handler);
+  if (object)
+    g_signal_handler_disconnect (object, handler);
 
   clipboard = gdk_display_get_clipboard (gdk_display_get_default ());