[gimp] app: unref the GtkSizeGroup-s.

[Jehan <jehanp src gnome org>]

commit 0fe7e147b5a8ffd0b8ca58d8d3cd60e202a80fbd
Author: Jehan <jehan girinstud io>
Date:   Sun Aug 22 11:50:48 2021 +0200

    app: unref the GtkSizeGroup-s.
    
    As explained in GTK docs, size groups are referenced by every internal
    widget hence can be immediately unref-ed after we added widgets in it.
    In the end, when the widgets are destroyed (thus removed from the
    group), the group will end up freed too.
    
    Reported by Massimo.

 app/dialogs/preferences-dialog.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/app/dialogs/preferences-dialog.c b/app/dialogs/preferences-dialog.c
index d34f732a96..d93c7102a5 100644
--- a/app/dialogs/preferences-dialog.c
+++ b/app/dialogs/preferences-dialog.c
@@ -3076,6 +3076,8 @@ prefs_dialog_new (Gimp       *gimp,
                                          GTK_LIST_BOX_ROW (row));
               }
           }
+        g_object_unref (name_group);
+        g_object_unref (format_group);
 
         g_signal_connect (listbox, "row-selected",
                           G_CALLBACK (prefs_format_string_select_callback),