极验异常时，处理空指针问题

src/main/java/cn/quantgroup/xyqb/service/captcha/GeetestLib.java

@@ -298,10 +298,10 @@ public class GeetestLib {
         }
         String return_seccode = "";
         try {
-            if (StringUtils.isNotEmpty(response)) {
+            JSONObject return_map = JSONObject.parseObject(response);
+            if (return_map == null) {
                 return val;
             }
-            JSONObject return_map = JSONObject.parseObject(response);
             return_seccode = return_map.getString("seccode");
             gtlog("md5: " + Md5Util.build(return_seccode));
             if (return_seccode.equals(Md5Util.build(seccode))) {