[gtk+/gtk-3-22] FileChooserButton: Avoid unref()ing a null model

[Daniel Boles <dboles src gnome org>]

commit b45aa63b756abbbcf2f493e72b980437ef84dd2f
Author: Daniel Boles <dboles src gnome org>
Date:   Fri Oct 6 21:34:03 2017 +0100

    FileChooserButton: Avoid unref()ing a null model
    
    Otherwise simply closing the widget-factory would give a critical from
    g_object_unref().

 gtk/gtkfilechooserbutton.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkfilechooserbutton.c b/gtk/gtkfilechooserbutton.c
index 957cf23..e5c0225 100644
--- a/gtk/gtkfilechooserbutton.c
+++ b/gtk/gtkfilechooserbutton.c
@@ -994,7 +994,8 @@ 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 != NULL)
+    g_object_unref (priv->model);
 
   G_OBJECT_CLASS (gtk_file_chooser_button_parent_class)->finalize (object);
 }