Fix possible turnaround overflow

[DL6ER]

What does this implement/fix?

Fix a value overflow in the rate-limiting diagnosis message reported on Discourse.

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Related issue or feature (if applicable): https://discourse.pi-hole.net/t/client-has-been-rate-limited-for-at-least-3217188-seconds/75091

Pull request in docs with documentation (if applicable): N/A

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2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/client-has-been-rate-limited-for-at-least-3217188-seconds/75091/9

[yubiuser]

Confirmed to fixe the issue
https://discourse.pi-hole.net/t/client-has-been-rate-limited-for-at-least-3217188-seconds/75091/10?u=yubiuser