It is possible for comments_per_page to be 0, which turns off pagination. See...

It is possible for comments_per_page to be 0, which turns off pagination. See sanitize_option(); wp_list_commnts(); get_comment_link(). see #17863.

git-svn-id: https://core.svn.wordpress.org/trunk@20202 1a063a9b-81f0-0310-95a4-ce76da25c4cd