[FIX] sale: pricelist price base

When setting a pricelist to show the public price discount, it ignored
the pricelist item's base field (if not 'Other Pricelist') and set it
by default on the lst_price instead.

This did not work when you based your discount on the standard_price
(= cost price) with public price discount.

Now it does.

opw: 775275

addons/sale/models/sale.py

@@ -857,7 +857,7 @@ class SaleOrderLine(models.Model):
             return price
         else:
             from_currency = self.order_id.company_id.currency_id
-            return from_currency.compute(product.lst_price, self.order_id.pricelist_id.currency_id)
+            return from_currency.compute(product[pricelist_item.base], self.order_id.pricelist_id.currency_id)
 
     @api.multi
     @api.onchange('product_id')