Posts, Post Types: Fail gracefully when checking whether the post should be...

Posts, Post Types: Fail gracefully when checking whether the post should be displayed in `WP_Query::get_posts()` against unregistered post status.

If the post status is not registered, assume it's not public.

Follow-up to [47178].

Props roytanck.
See #48653.
Built from https://develop.svn.wordpress.org/trunk@47179


git-svn-id: https://core.svn.wordpress.org/trunk@46979 1a063a9b-81f0-0310-95a4-ce76da25c4cd