Don't try to translate tags in WP_Theme::translate_header() if we are not in...

Don't try to translate tags in WP_Theme::translate_header() if we are not in the admin and get_theme_feature_list() isn't defined. see #20103.



git-svn-id: https://core.svn.wordpress.org/trunk@20668 1a063a9b-81f0-0310-95a4-ce76da25c4cd