Adjust [20557] and check only parent(), as it is more semantic. We don't care...

Adjust [20557] and check only parent(), as it is more semantic. We don't care if the theme considers itself to be a child theme, we care if it has a valid parent. see #20103.



git-svn-id: https://core.svn.wordpress.org/trunk@20559 1a063a9b-81f0-0310-95a4-ce76da25c4cd