Fix eager loading has_many association with a join

A has_many association ordering on a joined table would omit the join
when eager loaded.

    class Character < ActiveRecord::Base
      has_many :appearances, -> { joins(:books).order("books.published_on") }
    end

    Character.where(name: "Gandalf").includes(:appearances).first
    => SQLite3::SQLException: no such column: books.published_on:
      SELECT "appearances".* FROM "appearances"
      WHERE "appearances"."character_id" IN (1)
      ORDER BY "books"."published_on"