restore point: error="no base id map found from saved id or last restored PiTR"

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

1. create log backup
2. do full backup
3. run workload
4. do restore point
5. wait a moment
6. restore point again
```
Execute command {"command": " /br restore point "--storage" "s3://tmp/br-log-backup0fa9fd62-9b43-43eb-a15a-6cdf890ded6c/Log?access-key=xx&secret-access-key=xx&endpoint=xxx&force-path-style=true" "--pd" "http://downstream-pd.xxx:2379" "--restored-ts" "463858505902194726" "--start-ts" "463858266564722783" "--concurrency=8" "--check-requirements=false" "--checksum=true"", "timeout": "120m", "resource name": "br"}
```

### 2. What did you expect to see? (Required)
second restore point can success.

### 3. What did you see instead (Required)
second restore point failed:
```
[2026/01/27 02:10:41.566 +00:00] [INFO] [collector.go:77] ["restore log failed summary"] [error="no base id map found from saved id or last restored PiTR"] [errorVerbose="no base id map found from saved id or last restored PiTR\ngithub.com/pingcap/tidb/br/pkg/restore/log_client.(*LogClient).GetBaseIDMapAndMerge\n\t/workspace/source/tidb/br/pkg/restore/log_client/client.go:1061\ngithub.com/pingcap/tidb/br/pkg/task.buildAndSaveIDMapIfNeeded\n\t/workspace/source/tidb/br/pkg/task/stream.go:2221\ngithub.com/pingcap/tidb/br/pkg/task.restoreStream\n\t/workspace/source/tidb/br/pkg/task/stream.go:1621\ngithub.com/pingcap/tidb/br/pkg/task.RunStreamRestore\n\t/workspace/source/tidb/br/pkg/task/stream.go:1469\ngithub.com/pingcap/tidb/br/pkg/task.RunRestore\n\t/workspace/source/tidb/br/pkg/task/restore.go:1003\nmain.runRestoreCommand\n\t/workspace/source/tidb/br/cmd/br/restore.go:91\nmain.newStreamRestoreCommand.func1\n\t/workspace/source/tidb/br/cmd/br/restore.go:265\ngithub.com/spf13/cobra.(*Command).execute\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.9.1/command.go:1015\ngithub.com/spf13/cobra.(*Command).ExecuteC\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.9.1/command.go:1148\ngithub.com/spf13/cobra.(*Command).Execute\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.9.1/command.go:1071\nmain.main\n\t/workspace/source/tidb/br/cmd/br/main.go:42\nruntime.main\n\t/root/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.6.linux-amd64/src/runtime/proc.go:285\nruntime.goexit\n\t/root/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.6.linux-amd64/src/runtime/asm_amd64.s:1693"]
```

### 4. What is your TiDB version? (Required)

Release Version: v9.0.0-beta.2.pre-1125-g5ee2924
Edition: Community
Git Commit Hash: 5ee2924cb1a162d49daff0e96b43d8efe35528ff
Git Branch: HEAD
UTC Build Time: 2026-01-27 12:06:45
GoVersion: go1.25.6
Race Enabled: false
Check Table Before Drop: false
Store: tikv
Kernel Type: Classic