Canonical: Ensure a redirect for posts missing `postname` in a query with an ID.

If a site is using `/%post_id%/%postname%/` as permalink structure, and is missing the `postname`, the site  won't redirect to the appropriate URL. This change ensure that the redirect happens.

Fixes: #12456.
Props: Frank.Prendergast, dd32, Otto42, hlanggo, wonderboymusic, atimmer, seth17, calvin_ngan, Niresh12495, anbumz, SergeyBiryukov, donmhico.



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