fix(blooms): Fix panic in bloom gateway

[chaudum]

What this PR does / why we need it:

The slice of block queriers can contain nil values, which causes nip pointer dereference when calling Close() on them.

The regression was introduced with PR #13288

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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[grobinson-grafana]

LGTM as a hotfix! Can we avoid inserting nil values into the slice instead as a long-term fix or is there a good reason for doing that?

[chaudum]

LGTM as a hotfix! Can we avoid inserting nil values into the slice instead as a long-term fix or is there a good reason for doing that?

There is a reason why we have nil values in the slice: The block queriers are obtained from the bloom store based on a list of block refs, and the result list needs to match the order of the input list. nil values indicate that a block is not available for a given block ref.