[gimp] app: fix wrong unref-ing.

[Jehan <jehanp src gnome org>]

commit 2d123b8290609a01418876335bfced224e7e1e9d
Author: Jehan <jehan girinstud io>
Date:   Mon Jul 5 13:01:47 2021 +0200

    app: fix wrong unref-ing.
    
    Testing this middle-click opening of image by their PATH/URI in the
    toolbox, I realized there was a bug. The original author was obviously
    intending to unref the toolbox which was ref-ed when calling
    gtk_clipboard_request_text(), not freeing the toolbox context, which
    could have dire consequences!
    
    Fixes this CRITICAL:
    
    > g_object_unref: assertion 'G_IS_OBJECT (object)' failed

 app/widgets/gimptoolbox.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/app/widgets/gimptoolbox.c b/app/widgets/gimptoolbox.c
index b20aa622b8..6cb27dbf83 100644
--- a/app/widgets/gimptoolbox.c
+++ b/app/widgets/gimptoolbox.c
@@ -706,5 +706,5 @@ toolbox_paste_received (GtkClipboard *clipboard,
         }
     }
 
-  g_object_unref (context);
+  g_object_unref (toolbox);
 }