Containers should not consider the size of invisible items when computing their own bounding boxes.

This fixes issues related to the rulers container believing it was taller than it actually is, and possibly other issues also

libs/canvas/item.cc

@@ -777,6 +777,10 @@ Item::add_child_bounding_boxes() const
 
 	for (list<Item*>::const_iterator i = _items.begin(); i != _items.end(); ++i) {
 
+		if (!(*i)->visible()) {
+			continue;
+		}
+
 		boost::optional<Rect> item_bbox = (*i)->bounding_box ();
 
 		if (!item_bbox) {