[gtk/expander-ref-leak] Release an extra reference on GtkExpander:child

[Emmanuele Bassi <ebassi src gnome org>]

commit 237d2b8012c4e3db18a829d08f42309185016800
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Aug 24 01:11:15 2021 +0100

    Release an extra reference on GtkExpander:child
    
    The child of a GtkExpander is owned directly by the expander whenever
    the "expanded" flag is unset. If a GtkExpander is disposed while not
    expanded, we need to explicitly release the reference on the child
    widget that we own.

 gtk/gtkexpander.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/gtk/gtkexpander.c b/gtk/gtkexpander.c
index 00b9a52e38..bbe43eb255 100644
--- a/gtk/gtkexpander.c
+++ b/gtk/gtkexpander.c
@@ -582,6 +582,9 @@ gtk_expander_dispose (GObject *object)
       expander->expand_timer = 0;
     }
 
+  if (!expander->expanded)
+    g_clear_object (&expander->child);
+
   if (expander->box)
     {
       gtk_widget_unparent (expander->box);