With `map_meta_cap` enabled for a post type, the `read_post` capability for posts with a public status is supposed to be mapped to the post type's `read` capability.
When a post is left in the database after the post status is no longer present, and WP does a `read_post` check against it, a PHP notice was thrown, and the cap check always failed.
As a more graceful fallback, the cap is now mapped onto `edit_others_posts`, which allows highly privileged users to be able to access orphaned content.
A `_doing_it_wrong()` notice is also added, so that developers and site administrators are aware that the cap mapping is failing in the absence of the registered post status.
Follow-up to [34091], which introduced a similar approach to checking mapped caps against an unregistered post type.
Props roytanck, SergeyBiryukov.
Fixes#48653.
git-svn-id: https://develop.svn.wordpress.org/trunk@47178 602fd350-edb4-49c9-b593-d223f7449a82
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