fix: avoid tidb operator panic becuase of empty backup.Status.BackoffRetryStatus

[MarsBighead]

What problem does this PR solve?

What is changed and how does it work?

ref https://github.com/pingcap/tidb-operator/issues/5584

Fix tidb operator panic becuase of empty backup.Status.BackoffRetryStatus in multiple operators' case.

Code changes

• [x] Has Go code change
• [ ] Has CI related scripts change

Tests

• [ ] Unit test
• [ ] E2E test
• [ ] Manual test
• [ ] No code

Side effects

• [ ] Breaking backward compatibility
• [ ] Other side effects:

Related changes

• [ ] Need to cherry-pick to the release branch
• [ ] Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[sre-bot]

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[ti-chi-bot[bot]]

Welcome @MarsBighead! It looks like this is your first PR to pingcap/tidb-operator 🎉

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 61.53%. Comparing base (44eeb5f) to head (e2a87aa).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5597 +/- ## ========================================== + Coverage 61.48% 61.53% +0.05% ========================================== Files 235 246 +11 Lines 30336 34229 +3893 ========================================== + Hits 18651 21064 +2413 - Misses 9815 11190 +1375 - Partials 1870 1975 +105 ``` | [Flag](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5597/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [e2e](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5597/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `21.18% <100.00%> (?)` | | | [unittest](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5597/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `61.49% <0.00%> (+<0.01%)` | :arrow_up: |

[csuzhangxc]

/run-pull-e2e-kind-br

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: WangLe1321

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tidb-operator/blob/master/OWNERS)~~ [WangLe1321] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-03-29 09:32:48.628258224 +0000 UTC m=+4430.155798768: :ballot_box_with_check: agreed by WangLe1321.

[csuzhangxc]

/cherry-pick release-1.5

[ti-chi-bot]

@csuzhangxc: once the present PR merges, I will cherry-pick it on top of release-1.5 in the new PR and assign it to you.

In response to [this](https://github.com/pingcap/tidb-operator/pull/5597#issuecomment-2026968200): >/cherry-pick release-1.5 Instructions for interacting with me using PR comments are available [here](https://prow.tidb.net/command-help). If you have questions or suggestions related to my behavior, please file an issue against the [ti-community-infra/tichi](https://github.com/ti-community-infra/tichi/issues/new?title=Prow%20issue:) repository.

[ti-chi-bot]

@csuzhangxc: new pull request created to branch release-1.5: #5598.

In response to [this](https://github.com/pingcap/tidb-operator/pull/5597#issuecomment-2026968200): >/cherry-pick release-1.5 Instructions for interacting with me using PR comments are available [here](https://prow.tidb.net/command-help). If you have questions or suggestions related to my behavior, please file an issue against the [ti-community-infra/tichi](https://github.com/ti-community-infra/tichi/issues/new?title=Prow%20issue:) repository.