[bug] kiwi 出现空指针问题

### Is this a regression?

None

### Description

复现流程：
1、启动 2 个 KIWI 节点，其中一个执行 RAFT.CLUSTER join 127.0.0.1:9221 加入另一个节点，作为 follower 节点
2、往 leader 节点 set 几条数据
3、将 leader 进程关闭，过一会再重启
4、观察从节点一会，有可能出现如下问题
从下图线程名来看，是 brpc 触发的某个问题：

栈入口方法：

### Please provide a link to a minimal reproduction of the bug

_No response_

### Screenshots or videos


### Please provide the version you discovered this bug in (check about page for version information)

_No response_

### Anything else?

_No response_

Reproduce the two-node RAFT scenario described: join a follower, write data on the leader, stop and restart the leader, then observe the follower. Start from the stack-entry method shown in the attached screenshot; no source file or test is named. Done means the follower no longer encounters the reported null-pointer failure after leader recovery.

Written by the indexing model from the issue text.