In `wp_create_post_autosave()`, intersect the `$new_autosave`'s keys with the keys from `_wp_post_revision_fields()` to ensure that all expected fields are present.

Props kovshenin.
Fixes #25416.



git-svn-id: https://develop.svn.wordpress.org/trunk@27690 602fd350-edb4-49c9-b593-d223f7449a82