Fix max lsn bug

[jbajic]

Summary of changes

The problem it fixes is when request_lsn is u64::MAX-1 the cont_lsn becomes u64::MAX which is the same as prev_lsn which stops the loop.

Closes #6812

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• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
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Checklist before merging

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[VladLazar]

Hey - Thanks for the contribution! Looks correct to me.
Please remove the stray commented out lines mentioned in the comments.

[github-actions]

2496 tests run: 2373 passed, 0 failed, 123 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_lazy_attach_activation[delete]: debug

Code coverage* (full report)

• functions: 28.8% (7035 of 24445 functions)
• lines: 47.6% (43472 of 91383 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
6d2899c at 2024-03-12T10:41:53.361Z :recycle:}

[VladLazar]

@jbajic - just merged this. Thanks for the PR!