Accept Merge Request #1603: (feature/sale_order_route_pick -> develop)

Merge Request: 解决删除表面工艺，多增加了采购单的bug

Created By: @胡尧
Accepted By: @胡尧
URL: https://jikimo-hn.coding.net/p/jikimo_sfs/d/jikimo_sf/git/merge/1603

sf_manufacturing/models/mrp_workorder.py

@@ -331,7 +331,7 @@ class ResMrpWorkOrder(models.Model):
     def _get_surface_technics_purchase_ids(self):
         domain = [('origin', '=', self.production_id.name), ('purchase_type', '=', 'consignment')]
         purchase_orders = self.env['purchase.order'].search(domain)
-        purchase_orders_id = None
+        purchase_orders_id = self.env['purchase.order']
         for po in purchase_orders:
             for line in po.order_line:
                 if line.product_id.server_product_process_parameters_id == self.surface_technics_parameters_id: