window-list: Fix preferences radio buttons not reflecting the setting

When setting GtkRadioButton's group property, its active property is
also set as a by-product. This means that setting these properties
isn't commutative which arguably is a bug in gtk+ but one that we can
easily work around by just switching the order here.

https://bugzilla.gnome.org/show_bug.cgi?id=697495

extensions/window-list/prefs.js

@@ -59,9 +59,9 @@ const WindowListPrefsWidget = new GObject.Class({
                continue;
             }
 
-            radio = new Gtk.RadioButton({ group: radio,
+            radio = new Gtk.RadioButton({ active: currentMode == mode,
                                           label: label,
-                                          active: currentMode == mode });
+                                          group: radio });
             grid.add(radio);
 
             radio.connect('toggled', Lang.bind(this, function(button) {