iterator.go
func (it *Iterator) SeekToLast() {
	it.setNode(it.list.getPrev(it.list.tail, 0), true)
}
func (it *Iterator) SeekToLast() {
	it.setNode(it.list.getPrev(it.list.tail, 0), true)
}
// SeekToLast seeks position at the last entry in list.
// Final state of iterator is Valid() iff list is not empty.