修复关联订单 采购商Id条件错误

BBWYB.Server.Business/PurchaseOrder/PurchaseOrderBusiness.cs

@@ -576,7 +576,7 @@ namespace BBWYB.Server.Business
 
                         #region 处理采购商Id
                         var purchaserId = purchaseOrderSimpleInfo.PurchaserId;
-                        if (!string.IsNullOrEmpty(purchaserId))
+                        if (string.IsNullOrEmpty(purchaserId))
                             throw new BusinessException($"采购单{purchaseOrder.PurchaseOrderId}缺少采购商Id");
                         purchaserId = purchaserId.Replace("b2b-", string.Empty);
                         var purchaserId2 = purchaserId.Substring(0, purchaserId.Length - 5);