[dia] element: don't set a free func

[Zander Brown <zbrown src gnome org>]

commit 51ef0dece7b4ec99c4a812196928f0581f7f22c6
Author: Zander Brown <zbrown gnome org>
Date:   Tue Jul 21 02:11:30 2020 +0100

    element: don't set a free func
    
    Fix https://gitlab.gnome.org/GNOME/dia/-/issues/451

 lib/element.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/lib/element.c b/lib/element.c
index cad03feb..2843e6ac 100644
--- a/lib/element.c
+++ b/lib/element.c
@@ -604,7 +604,7 @@ element_change_new (const Point *corner,
 
   ec->object_change.apply  = _element_change_swap;
   ec->object_change.revert = _element_change_swap;
-  ec->object_change.free = (ObjectChangeFreeFunc) g_free;
+  ec->object_change.free = NULL;
 
   ec->element = elem;
   ec->corner = elem->corner;