wp_list_pages() creates empty <ul> tags with depth=1 argument

[fitztrev]

When a page has a child page, and the user wants to display just the top level pages, this is the syntax to use:

<?php wp_list_pages('depth=1'); ?>

However, this creates pairs of "<ul></ul>"s where those children would normally be nested beneath the parents.

[hailin]

patch file

[hailin]

fixed and tested on wporg and wpcom, by examining "view source".
It works correctly now.

[ryan]

(In [6388]) Fix depth = 1 page traversal. Props hailin. fixes #5469