Fix possible race condition in Top Lists

[DL6ER]

What does this implement/fix?

Fix possible race condition on page load of the index page. This is a recent regression by #3058

Reported on Discourse https://discourse.pi-hole.net/t/double-and-duplicate-items-in-all-the-top-categories/70969

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Related issue or feature (if applicable): N/A

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

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