fix: avoid tidb operator panic becuase of empty backup.Status.BackoffRetryStatus (#5597)

[ti-chi-bot]

This is an automated cherry-pick of #5597

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.

[ti-chi-bot[bot]]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 61.54%. Comparing base (f3da06b) to head (693e59b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-1.5 #5598 +/- ## =============================================== - Coverage 61.56% 61.54% -0.02% =============================================== Files 229 229 Lines 29330 29330 =============================================== - Hits 18056 18051 -5 - Misses 9495 9498 +3 - Partials 1779 1781 +2 ``` | [Flag](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5598/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [unittest](https://app.codecov.io/gh/pingcap/tidb-operator/pull/5598/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | `61.54% <0.00%> (-0.02%)` | :arrow_down: |