Apply checks in [27964] to wp_write_post(), which is unused and due for dismantling and deprecation.

see #27452.

Built from https://develop.svn.wordpress.org/trunk@27975


git-svn-id: http://core.svn.wordpress.org/trunk@27805 1a063a9b-81f0-0310-95a4-ce76da25c4cd