br: fix get snapshot response pointer deref panic (#54510)

[ti-chi-bot]

This is an automated cherry-pick of #54510

What problem does this PR solve?

Issue Number: close #54511

Problem Summary:

EC2 DescribeSnapshots API doesn't always return StateMessage in response for errored snapshot. Example response:

{
    "Snapshots": [
        {
            "Description": "",
            "Encrypted": true,
            "KmsKeyId": "...",
            "OwnerId": "...",
            "Progress": "99%",
            "SnapshotId": "snap-04c5f87d0a2b069b0",
            "StartTime": "2024-07-08T15:07:01.437000+00:00",
            "State": "error",
            "VolumeId": "vol-0377214577dd710de",
            "VolumeSize": 50,
            "Tags": [
                ...
            ],
            "StorageTier": "standard"
        }
    ]
}

In these cases, snapshot backup process panics due to nil pointer dereference. End result is the same (failed backup), but we still want to correctly process these errors

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4474931]

goroutine 1 [running]:
github.com/pingcap/tidb/br/pkg/aws.(*EC2Session).WaitSnapshotsCreated(0xc03e03f660, 0xc0073997d0, {0x5c81370, 0xc00c4a6b00})
  /tidb/br/pkg/aws/ebs.go:255 +0xa71
github.com/pingcap/tidb/br/pkg/task.RunBackupEBS({0x5c814f8, 0xc000193b80}, {0x5c940b8?, 0x86bcdc0?}, 0xc000c1fc00)
  /tidb/br/pkg/task/backup_ebs.go:255 +0x1c8a
main.runBackupCommand(0xc000c20000, {0x53bfc8f, 0xb})
  /tidb/br/cmd/br/backup.go:36 +0x1d4
main.newFullBackupCommand.func1(0xc00079a800?, {0xc000c480c0?, 0x4?, 0x53adfc5?})
  /tidb/br/cmd/br/backup.go:117 +0x1f
github.com/spf13/cobra.(*Command).execute(0xc000c20000, {0xc00026e030, 0xc, 0xc})
  /go/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:916 +0x87c
github.com/spf13/cobra.(*Command).ExecuteC(0xc000c04000)
  /go/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:1044 +0x3a5
github.com/spf13/cobra.(*Command).Execute(...)
  /go/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:968
main.main()
  /tidb/br/cmd/br/main.go:36 +0x212

What changed and how does it work?

Check state message ptr is defined before deref

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

test panics prior to fix, success w/ fix

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, YuJuncen

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• OWNERS [YuJuncen]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-28 06:01:05.394107704 +0000 UTC m=+936460.528557826: ☑️ agreed by BornChanger.
• 2024-08-28 06:06:23.657272125 +0000 UTC m=+936778.791722247: ☑️ agreed by YuJuncen.

[codecov]

Codecov Report

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Additional details and impacted files

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