Improved array handling for post type. - @unr

There was an error with using arrays as a post type in a query with Yoast, which was fixed here https://github.com/Yoast/wordpress-seo/commit/99177ffc35f88bdc514135ac9dc50792d604a438

However, there was one more instance that was not fixed as well. This PR cleans up that other instance.


![selfie-2](http://i.imgur.com/vqTLd7x.gif)