Window: allow removing the toolbar_box

Allow the toolbar_box to be removed by setting it to None, like is supported
for canvas.

Signed-off-by: Sascha Silbe <silbe@activitycentral.com>
Acked-by: Simon Schampijer <simon@laptop.org>

src/sugar/graphics/window.py

@@ -191,8 +191,9 @@ class Window(gtk.Window):
         if self._toolbar_box:
             self.__vbox.remove(self._toolbar_box)
 
-        self.__vbox.pack_start(toolbar_box, False)
-        self.__vbox.reorder_child(toolbar_box, 0)
+        if toolbar_box:
+            self.__vbox.pack_start(toolbar_box, False)
+            self.__vbox.reorder_child(toolbar_box, 0)
 
         self._toolbar_box = toolbar_box