Check that the class is actually a user

[stafflink-web-services]

Adds a check before getting the user meta_type and ensuring it's a user before proceeding with the user.

In some instances, Rank Math is catching a custom post type if other plugins are involved. For example, sometimes the post object is being fed into the class-user, and this object does not have a 'meta_type', causing a fatal error in PHP 8+.

[mattneal-stafflink]

Cancel this one. I'm an idiot. One of my devs were doing something super small but super silly, so I went on a long path trying to fix something that wasn't broken. Ignore this request.