[gtk+] GtkScrolledWindow: Add some NULL checks back

[Matthias Clasen <matthiasc src gnome org>]

commit 8817fa9e3dd7fcc08ef64eb6c2b74a04fa3aa192
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu May 29 21:52:40 2014 -0400

    GtkScrolledWindow: Add some NULL checks back
    
    Turns out these were not quite redundant, gtk_container_forall
    may be called very early during construction.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=730924

 gtk/gtkscrolledwindow.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index f17d58f..9aad13a 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1664,8 +1664,10 @@ gtk_scrolled_window_forall (GtkContainer *container,
       scrolled_window = GTK_SCROLLED_WINDOW (container);
       priv = scrolled_window->priv;
 
-      callback (priv->vscrollbar, callback_data);
-      callback (priv->hscrollbar, callback_data);
+      if (priv->vscrollbar)
+        callback (priv->vscrollbar, callback_data);
+      if (priv->hscrollbar)
+        callback (priv->hscrollbar, callback_data);
     }
 }