Add index panic in a cluster with multiple TiDB instances

[tangenta]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Prepare a cluster with multiple TiDB instances.
2. Prepare a small data set.
3. Add index for one of the table.

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

No error.

3. What did you see instead (Required)

[2023/11/07 12:14:04.903 +08:00] [ERROR] [spool.go:139] ["recover panic"] [recover="runtime error: index out of range [0] with length 0"] [s
run.func1.1
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/resourcemanager/pool/spool/spoolgo:139
runtime.gopanic
/usr/local/go/src/runtime/panic.go:914
runtime.goPanicIndex
/usr/local/go/src/runtime/panic.go:114
github.com/pingcap/tidb/pkg/ddl.generateNonPartitionPlanh
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/ddl/backfilling_dispatcher.go:3222
github.com/pingcap/tidb/pkg/ddl.(*BackfillingDispatcherExt).OnNextSubtasksBatch
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/ddl/backfilling_dispatcher.go:1633
github.com/pingcap/tidb/pkg/disttask/framework/dispatcher.(*BaseDispatcher).onNextStage
/home/jenkins/agent/workspace/build-common/go/src/github.comm/pingcap/tidb/pkg/disttask/framework/dispatcher/dispatcher.0:54
github.com/pingcap/tidb/pkg/disttask/framework/dispatcher.(*BaseDispatcher).onPending
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/dspatcher.go:319
github.com/pingcap/tidb/pkg/disttask/framework/dispatcher.(BaseDispatcher).scheduleTask
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/dispatcher.go:212
github.com/pingcap/tidb/pkg/disttask/framework/dispatcher. (*BaseDispatcher).ExecuteTask
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/dspatcher.go:132
github.com/pingcap/tidb/pkg/disttask/framework/dispatcher.(*Manag(er).dispatchTaskLoop.(*Manager).startDispatcher.func
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/disttask/framework/dispatcher/dispatcher_manager.go:285
github.com/pingcap/tidb/pkg/resourcemanager/pool/spool.(*Pool).run.funcl
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/pkg/resourcemanager/pool/spool/spoolgo:144"]

4. What is your TiDB version? (Required)

662528d