[#1973] Fixed accounts rendering in GET /api/v1/pleroma/chats with truish :restrict_unauthenticated setting

Closes #1973 (closed)

Fixed accounts rendering in GET /api/v1/pleroma/chats with truish :restrict_unauthenticated (having local: true and/or remote: true contents under profiles key).

Made Pleroma.Web.MastodonAPI.AccountView.render("show.json", _) demand :for or :force option in order to prevent incorrect rendering of empty map instead of expected user representation with truish :restrict_unauthenticated setting.

The issue was caused by calling AccountView.render("show.json", _) without :for option which was previously interpreted as for: nil and was mistreated as a request to render for an anonymous user (which was denied by :restrict_unauthenticated setting).