Merge pull request liukuo362573#120 from LiYinJiang/dev

对于无权限用户登录后跳转到/Home/NoPermission页面后，response.CharacterSet存在NPE。补充判断避免直接崩溃

YiSha.Util/YiSha.Util/HttpHelper.cs

@@ -208,7 +208,7 @@ private HttpResult GetHttpRequestData(HttpItem httpItem)
                         }
                         else
                         {
-                            if (response.CharacterSet.ToLower().Trim() == "iso-8859-1")
+                            if (response.CharacterSet !=null && response.CharacterSet.ToLower().Trim() == "iso-8859-1")
                             {
                                 encoding = Encoding.GetEncoding("gbk");
                             }