can not start tidb-server while using plugin

[aytrack]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

./bin/tidb-server -plugin-load="whitelist-1,audit-1" -plugin-dir="/root/plugins/bin/"

2. What did you expect to see? (Required)

tidb-server started and plugin load success

3. What did you see instead (Required)

tidb-server can not start

2022/08/23 20:43:04.848 +08:00] [INFO] [delete_range.go:140] ["[ddl] start delRange emulator"]
[2022/08/23 20:43:04.848 +08:00] [INFO] [ddl_worker.go:165] ["[ddl] start DDL worker"] [worker="worker 1, tp general"]
[2022/08/23 20:43:04.848 +08:00] [INFO] [ddl_worker.go:165] ["[ddl] start DDL worker"] [worker="worker 2, tp add index"]
[2022/08/23 20:43:04.849 +08:00] [WARN] [sysvar_cache.go:52] ["sysvar cache is empty, triggering rebuild"]
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x88 pc=0x7f234549fd21]

goroutine 1 [running]:
github.com/pingcap/tidb/session.(*domainMap).Get(0x6495a60, {0x0, 0x0})
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/tidb.go:52 +0x61
github.com/pingcap/tidb/session.GetDomain(...)
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/session.go:2926
github.com/pingcap/enterprise-plugin/whitelist.(*handle).init(0x7f2347fbcac0)
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/enterprise-plugin/whitelist/whitelist.go:188 +0xf8
github.com/pingcap/enterprise-plugin/whitelist.OnInit({0x3870dc0?, 0xc000914660?}, 0x30?)
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/enterprise-plugin/whitelist/whitelist.go:33 +0x25
github.com/pingcap/tidb/plugin.Init({0x42a6800, 0xc000054078}, {{0x0, 0x0, 0x0}, {0x0, 0x0}, 0x0, 0x0, 0x0})
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/plugin/plugin.go:209 +0x209
github.com/pingcap/tidb/session.BootstrapSession({0x42c2e00, 0xc000633100})
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/session.go:2880 +0x67d
main.createStoreAndDomain()
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/tidb-server/main.go:296 +0x114
main.main()
        /home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/tidb-server/main.go:202 +0x4ca

4. What is your TiDB version? (Required)

sh-4.2# ./bin/tidb-server -V
Release Version: v6.1.1
Edition: Community
Git Commit Hash: 1f7e2ce63ddddd5e772e7f4efa17492d2017ed26
Git Branch: heads/refs/tags/v6.1.1
UTC Build Time: 2022-08-23 08:30:42
GoVersion: go1.18.5
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

sh-4.2# cat *.md5
887a614f3bca86d06be698a274b09d85  audit/audit-1.so
1b944c57ef8a479bbd4130ebb5e4eb45  whitelist/whitelist-1.so

[xhebox]

Introduced by #36792, will be fixed by #37321