[gtk+/gtk-3-14] GtkBox: Ensure we only allow one center child

[Matthias Clasen <matthiasc src gnome org>]

commit 1670ba1d511a6e7e90ca7002ed6bbe80db7f1895
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Oct 13 12:44:02 2014 -0400

    GtkBox: Ensure we only allow one center child
    
    Glade was happily adding multiple center widgets. Oops.

 gtk/gtkbox.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkbox.c b/gtk/gtkbox.c
index 613b5ae..72f26e9 100644
--- a/gtk/gtkbox.c
+++ b/gtk/gtkbox.c
@@ -2619,10 +2619,14 @@ gtk_box_set_center_widget (GtkBox    *box,
 
   g_return_if_fail (GTK_IS_BOX (box));
 
+  if (priv->center)
+    {
+      gtk_box_remove (GTK_CONTAINER (box), priv->center->widget);
+      priv->center = NULL;
+    }
+
   if (widget)
     priv->center = gtk_box_pack (box, widget, FALSE, TRUE, 0, GTK_PACK_START);
-  else if (priv->center)
-    gtk_box_remove (GTK_CONTAINER (box), priv->center->widget);
 }
 
 /**