title: I cannot add a product in PrestaShop v1.6.1.0
body: <p>I can't add product in back office. Prestashop 1.6.1.0 throws exception:</p>
  
  <blockquote>
    <p>Unknown column 'product_attribute_shop.id_product' in 'on clause'</p>
  </blockquote>
  
  <pre><code>SELECT product_shop.id_product,
         Ifnull(product_attribute_shop.id_product_attribute, 0)
         id_product_attribute
  FROM   `ps_product_reductions` pr,
         `ps_product` p
         INNER JOIN ps_product_shop product_shop
                 ON ( product_shop.id_product = p.id_product
                      AND product_shop.id_shop = 1 )
         LEFT JOIN `ps_product_attribute_shop` product_attribute_shop
                ON ( p.`id_product` = product_attribute_shop.`id_product`
                     AND product_attribute_shop.`default_on` = 1
                     AND product_attribute_shop.id_shop = 1 )
  WHERE  p.id_product = pr.id_product
         AND ( pr.id_product_attribute = 0
                OR product_attribute_shop.id_product_attribute =
             pr.id_product_attribute )
         AND product_shop.`active` = 1
         AND EXISTS(SELECT 1
                    FROM   `ps_category_product` cp
                           JOIN `ps_category_group` cg
                             ON ( cp.id_category = cg.id_category
                                  AND cg.`id_group` = 1 )
                    WHERE  cp.`id_product` = p.`id_product`)
         AND product_shop.`visibility` IN ( "both", "catalog" )
  ORDER  BY Rand()
  LIMIT  1 
  </code></pre>