Remove unnecessary loops in default-filters.php.

props Jayjdk.
fixes #25011.

Built from https://develop.svn.wordpress.org/trunk@25134


git-svn-id: http://core.svn.wordpress.org/trunk@25114 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Only show 'Preview' on the custom header screen if there is something to show.

props nickmomrik.
fixes #14531.

Built from https://develop.svn.wordpress.org/trunk@25135


git-svn-id: http://core.svn.wordpress.org/trunk@25115 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Ensure a user exists in get_comment_author().

props azaozz.
see #24084.

Built from https://develop.svn.wordpress.org/trunk@25136


git-svn-id: http://core.svn.wordpress.org/trunk@25116 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Initialize kses filters if _wp_unfiltered_html_comment nonce isn't set.

See #24752.

Built from https://develop.svn.wordpress.org/trunk@25137


git-svn-id: http://core.svn.wordpress.org/trunk@25117 1a063a9b-81f0-0310-95a4-ce76da25c4cd