Wait list autofill should not occur if registration is closed for the host entity

Problem/Motivation

If a registration is canceled or deleted after the host entity is closed for registration, autofill should not occur. For example, if an administrator is cleaning up the registration history for an event that occurred 3 month ago, registrations should not be moved off the wait list and into complete state, as this could trigger confirmation emails that welcome someone to a past event.

Steps to reproduce

Cancel a completed registration for a past event that has wait listed registrations and the host entity is configured to autofill. One of the wait listed registrations will automatically fill the open spot.

Proposed resolution

Ensure the host entity is enabled for registration before autofilling.