br: fix lightning checksum panic and speed up pre-check

[glorv]

What problem does this PR solve?

cherry-pick #27596 and #27607 into release-5.2-20210908

Issue Number: close #xxx

Problem Summary:

What is changed and how it works?

Proposal: xxx

What's Changed:

How it Works:

Check List

Tests

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

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

None

[ti-chi-bot]

@glorv: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• gozssky
• lance6716

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