Use OrderArticle#create in receive form instead of Order#add_article

app/controllers/order_articles_controller.rb

@@ -16,7 +16,7 @@ class OrderArticlesController < ApplicationController
     #   given mentioning that the article already exists, which is desired.
     @order_article = @order.order_articles.where(:article_id => params[:order_article][:article_id]).first
     if @order_article and @order_article.units_to_order == 0
-      @order_article.units_to_order = 1
+      @order_article.units_to_order = 1 # FIXME: this is ugly if used in the receive form
     else
       @order_article = OrderArticle.new(params[:order_article])
     end