[gtk+] FileChooserButton: Avoid unref()ing a null model

[Daniel Boles <dboles src gnome org>]

commit c1a5afb3a824bd0691484be72f534d2f0ba6ef22
Author: Daniel Boles <dboles src gmail com>
Date:   Sat Oct 7 00:09:09 2017 +0100

    FileChooserButton: Avoid unref()ing a null model

 gtk/gtkfilechooserbutton.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkfilechooserbutton.c b/gtk/gtkfilechooserbutton.c
index abc6147..c5b58a5 100644
--- a/gtk/gtkfilechooserbutton.c
+++ b/gtk/gtkfilechooserbutton.c
@@ -1061,7 +1061,8 @@ gtk_file_chooser_button_finalize (GObject *object)
   if (priv->current_folder_while_inactive)
     g_object_unref (priv->current_folder_while_inactive);
 
-  g_object_unref (priv->model);
+  if (priv->model)
+    g_object_unref (priv->model);
 
   gtk_widget_unparent (priv->button);
   gtk_widget_unparent (priv->combo_box);