用户不需要验证码的时候刷新验证会导致错误，增加判断

static/src/js/app/oj/account/login.js

@@ -33,7 +33,9 @@ require(["jquery", "bsAlert", "csrfToken", "validator"], function ($, bsAlert, c
                         location.href = "/";
                     }
                     else {
-                        refresh_captcha();
+                        if(applied_captcha) {
+                            refresh_captcha();
+                        }
                         bsAlert(data.data);
                     }
                 }