A child theme with a missing parent might be is_child_theme() but not have a...

A child theme with a missing parent might be is_child_theme() but not have a valid parent() object, so we need to check parent() too. see #20103.



git-svn-id: https://core.svn.wordpress.org/trunk@20558 1a063a9b-81f0-0310-95a4-ce76da25c4cd