Return 404 NotFound error if ChatChannelMembership is not found

[mstruve]

In our chat_channel_memberships_controller.rb are look for a membership and then attempt to authorize it. In the event that the membership is missing we end up with the following error.
Honeybadger: https://app.honeybadger.io/fault/66984/aa161bc85a5f59b582b7949c2a14d83c
Error:

Pundit::NotDefinedError: unable to find policy `NilClassPolicy` for `nil`
chat_channel_memberships_controller.rb  6 find_by_chat_channel_id(...)
[PROJECT_ROOT]/app/controllers/chat_channel_memberships_controller.rb:6:in `find_by_chat_channel_id'
4   def find_by_chat_channel_id
5     @membership = ChatChannelMembership.where(chat_channel_id: params[:chat_channel_id], user_id: current_user.id).first
6     authorize @membership
7     render json: @membership.to_json(
8       only: %i[id status viewable_by chat_channel_id last_opened_at],

Rather than raising Pundit::NotDefinedError here we should be returning a 404, not_found status. ApplicationController has a handy not_found method that you can use to do this. I think you will want to implement a solution similar to this one.

[majakomel]

I'll work on this 🙋🏼‍♀️