TiDB panic during lightning logical import

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1. lightning tidb backend import

### 2. What did you expect to see? (Required)
1. Import should succeed

### 3. What did you see instead (Required)
Lightning import failed, tidb panic seen

```
[2023/10/10 04:46:39.934 +00:00] [ERROR] [table_import.go:526] ["import whole table failed"] [table=`bigc`.`t`] [takeTime=40m52.405135307s] [error="[`bigc`.`t`] batch write rows reach max retry 3 and still failed: dial tcp 10.233.53.181:4000: connect: connection refused"]
[2023/10/10 04:46:39.934 +00:00] [ERROR] [import.go:1684] ["failed to import table"] [table=`bigc`.`t`] [error="[`bigc`.`t`] batch write rows reach max retry 3 and still failed: dial tcp 10.233.53.181:4000: connect: connection refused"] [errorVerbose="dial tcp 10.233.53.181:4000: connect: connection refused\ngithub.com/pingcap/errors.AddStack\n\t/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20221009092201-b66cddb77c32/errors.go:174\ngithub.com/pingcap/errors.Trace\n\t/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20221009092201-b66cddb77c32/juju_adaptor.go:15\ngithub.com/pingcap/tidb/br/pkg/lightning/backend/tidb.(*tidbBackend).execStmts\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/backend/tidb/tidb.go:761\ngithub.com/pingcap/tidb/br/pkg/lightning/backend/tidb.(*tidbBackend).WriteBatchRowsToDB\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/backend/tidb/tidb.go:667\ngithub.com/pingcap/tidb/br/pkg/lightning/backend/tidb.(*tidbBackend).WriteRows\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/backend/tidb/tidb.go:617\ngithub.com/pingcap/tidb/br/pkg/lightning/backend/tidb.(*Writer).AppendRows\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/backend/tidb/tidb.go:862\ngithub.com/pingcap/tidb/br/pkg/lightning/importer.(*chunkProcessor).deliverLoop.func1\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/importer/chunk_process.go:657\ngithub.com/pingcap/tidb/br/pkg/lightning/importer.(*chunkProcessor).deliverLoop\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/importer/chunk_process.go:681\ngithub.com/pingcap/tidb/br/pkg/lightning/importer.(*chunkProcessor).process.func1\n\t/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/br/br/pkg/lightning/importer/chunk_process.go:198\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1650\n[`bigc`.`t`] batch write rows reach max retry 3 and still failed"]
[2023/10/10 04:46:39.935 +00:00] [ERROR] [import.go:1688] ["restore table failed"] [table=`bigc`.`t`] [takeTime=40m52.40835841s] [error="[Lightning:Restore:ErrRestoreTable]restore table `bigc`.`t` failed: [`bigc`.`t`] batch write rows reach max retry 3 and still failed: dial tcp 10.233.53.181:4000: connect: connection refused"]

```
```
kubectl --kubeconfig kubeconfig.yml -n cdc-kafka-scale-cdc-scale-tps-3030040-1-444 logs -p upstream-tidb-1
start tidb-server ...
/tidb-server --store=tikv --advertise-address=upstream-tidb-1.upstream-tidb-peer.cdc-kafka-scale-cdc-scale-tps-3030040-1-444.svc --host=[0.0.0.0](http://0.0.0.0/) --path=upstream-pd:2379 --config=/etc/tidb/tidb.toml

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x128 pc=0x4c3a1e9]

goroutine 23368311 [running]:
[github.com/pingcap/tidb/server.(*rpcServer).KvPrewrite](http://github.com/pingcap/tidb/server.(*rpcServer).KvPrewrite)(0x5601b40?, {0x60b7ac0?, 0xc0163df4d0?}, 0x0?)
:1 +0x29
[github.com/pingcap/kvproto/pkg/tikvpb._Tikv_KvPrewrite_Handler](http://github.com/pingcap/kvproto/pkg/tikvpb._Tikv_KvPrewrite_Handler)({0x56f8880?, 0xc003e61740}, {0x60b7ac0, 0xc0163df4d0}, 0xc00296b880, 0x0)
/go/pkg/mod/[github.com/pingcap/kvproto@v0.0.0-20230904082117-ecdbf1f8c130/pkg/tikvpb/tikvpb.pb.go:2693](http://github.com/pingcap/kvproto@v0.0.0-20230904082117-ecdbf1f8c130/pkg/tikvpb/tikvpb.pb.go:2693) +0x16c
[google.golang.org/grpc.(*Server).processUnaryRPC](http://google.golang.org/grpc.(*Server).processUnaryRPC)(0xc001dd2b40, {0x60d63a0, 0xc009ec51e0}, 0xc00b56fe60, 0xc003e61860, 0x873b9f0, 0x0)
/go/pkg/mod/[google.golang.org/grpc@v1.54.0/server.go:1345](http://google.golang.org/grpc@v1.54.0/server.go:1345) +0xde7
[google.golang.org/grpc.(*Server).handleStream](http://google.golang.org/grpc.(*Server).handleStream)(0xc001dd2b40, {0x60d63a0, 0xc009ec51e0}, 0xc00b56fe60, 0x0)
/go/pkg/mod/[google.golang.org/grpc@v1.54.0/server.go:1722](http://google.golang.org/grpc@v1.54.0/server.go:1722) +0x9e7
[google.golang.org/grpc.(*Server).serveStreams.func1.2()](http://google.golang.org/grpc.(*Server).serveStreams.func1.2())
/go/pkg/mod/[google.golang.org/grpc@v1.54.0/server.go:966](http://google.golang.org/grpc@v1.54.0/server.go:966) +0x8d
created by [google.golang.org/grpc.(*Server).serveStreams.func1](http://google.golang.org/grpc.(*Server).serveStreams.func1) in goroutine 23368202
/go/pkg/mod/[google.golang.org/grpc@v1.54.0/server.go:964](http://google.golang.org/grpc@v1.54.0/server.go:964) +0x246
```

### 4. What is your TiDB version? (Required)
[root@upstream-tidb-0 /]# /tidb-server -V
Release Version: v7.4.0
Edition: Community
Git Commit Hash: 04ac2000e640cee9685ea288c5a2851d765ed28e
Git Branch: heads/refs/tags/v7.4.0
UTC Build Time: 2023-10-09 09:17:37
GoVersion: go1.21.1
Race Enabled: false
Check Table Before Drop: false
Store: unistore