[gtk+] header bar: Don't leave a dangling pointer

[Matthias Clasen <matthiasc src gnome org>]

commit 565677a22c6fb1af4ae153ce2299e3faf7484b33
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Sep 29 15:15:06 2015 -0400

    header bar: Don't leave a dangling pointer
    
    This might be the cause for some crashes, like
    https://bugzilla.redhat.com/show_bug.cgi?id=1264558

 gtk/gtkheaderbar.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkheaderbar.c b/gtk/gtkheaderbar.c
index 9e81d31..7589e1f 100644
--- a/gtk/gtkheaderbar.c
+++ b/gtk/gtkheaderbar.c
@@ -299,6 +299,8 @@ _gtk_header_bar_update_window_buttons (GtkHeaderBar *bar)
       priv->titlebar_end_separator = NULL;
     }
 
+  priv->titlebar_icon = NULL;
+
   if (!priv->shows_wm_decorations)
     return;