[nautilus/gnome-3-20] window: fix missing casting

[Carlos Soriano Sánchez <csoriano src gnome org>]

commit f9bc36a6bbb905c53750deed481d380e31b8b662
Author: Carlos Soriano <csoriano gnome org>
Date:   Mon Feb 15 11:05:41 2016 +0100

    window: fix missing casting
    
    https://bugzilla.gnome.org/show_bug.cgi?id=761965

 src/nautilus-window.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/nautilus-window.c b/src/nautilus-window.c
index 3a4aea3..29e499b 100644
--- a/src/nautilus-window.c
+++ b/src/nautilus-window.c
@@ -2446,7 +2446,7 @@ nautilus_window_init (NautilusWindow *window)
         * specific styling for nautilus without affecting other gtk+ applications.
         * This was a request by some theme authors.
         */
-       gtk_style_context_add_class (gtk_widget_get_style_context (window),
+       gtk_style_context_add_class (gtk_widget_get_style_context (GTK_WIDGET (window)),
                                     "nautilus-window");
 
        window_group = gtk_window_group_new ();