Comments pagination breaks with custom Kaminari page method.

[SirRawlins]

Expected behaviour

The paginated comments feature introduced in #5088 should render paginated comments even when using a custom Kaminari 'page_method_name', which may be used to prevent conflicts with will_paginate, as described in the documentation.

Actual behavior

Trying to render comments since #5088 raises an exception "undefined method `page' for #<ActiveRecord::Relation []>"

How to reproduce

Configure a custom Kaminari page method in config/initializers/kaminari.rb like so:

Kaminari.configure do |config|
    config.page_method_name = :per_page_kaminari
end

Try to render comments with active_admin_comments and watch it raise the exception.