Handle tally cases where `results` is `None`

Fixes

Fixes #1131 by @AetherUnbound

Description

This PR initializes results_to_tally to either results or [] so that any operations on it which assume it's a list will behave correctly.

Testing Instructions

Check out commit 65f2df5b8540eaae4ae2d7a40474620f3b5e5c72 and run just api-test - tests should fail and emulate current behavior
Check out the tip of this branch and run just api-test - tests should now pass!

Checklist

[x] My pull request has a descriptive title (not a vague title like Update index.md).
[x] My pull request targets the default branch of the repository (main) or a parent feature branch.
[x] My commit messages follow [best practices][best_practices].
[x] My code follows the established code style of the repository.
[x] I added or updated tests for the changes I made (if applicable).
[x] I added or updated documentation (if applicable).
[x] I tried running the project locally and verified that there are no visible errors.

[best_practices]: https://git-scm.com/book/en/v2/Distributed-Git-Contributing-to-a-Project#_commit_guidelines

Developer Certificate of Origin

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WordPress / openverse-api