[sysprof] util: clear field when destroying

[Christian Hergert <chergert src gnome org>]

commit b142d79bdc12e156f5e2df28a3c697e31d1d7e35
Author: Christian Hergert <chergert redhat com>
Date:   Fri Nov 24 00:35:42 2017 -0800

    util: clear field when destroying
    
    Just to be a bit more defensive.

 lib/util/sp-model-filter.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/lib/util/sp-model-filter.c b/lib/util/sp-model-filter.c
index 5bdd1f7..0dcf390 100644
--- a/lib/util/sp-model-filter.c
+++ b/lib/util/sp-model-filter.c
@@ -92,6 +92,7 @@ element_free (gpointer data)
 {
   Element *e = data;
 
+  e->iter = NULL;
   g_clear_object (&e->object);
   g_slice_free (Element, e);
 }