[FIX] website_quote: fix due to module migration

Coming from https://github.com/odoo/odoo/commit/232eea36ab98eb268f712b2083c637a7cb463e2c

addons/website_quote/models/sale_order.py

@@ -231,7 +231,7 @@ class SaleOrderOption(models.Model):
         if order.state not in ['draft', 'sent']:
             return False
 
-        order_line = self.order_line.filtered(lambda line: line.product_id == self.product_id)
+        order_line = order.order_line.filtered(lambda line: line.product_id == self.product_id)
         if order_line:
             order_line[0].product_uom_qty += 1
         else: