Fix status report page

[furai]

Description of the Change

Fixes the bug with status report page throwing an error when indexable post types returns an empty array. Closes #3909

How to test the Change

Add ep_indexable_post_types filter that returns an empty array.

Changelog Entry

Fixed - Status report page when indexable post types is an empty array.

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [x] All new and existing tests pass.

[furai]

I'll check if I can cover this in a test case and edit the main post accordingly.

EDIT: I could probably do it but definitely not today. I've been looking into whole setup and it's a bit complicated for a new contributor like me. I'd appreciate if any contributor could chime in and maybe add these extra tests if required for me. Maybe it's possible to merge this PR without extra tests cause it's really minor patch.

[felipeelia]

Thanks for the PR @furai!

[furai]

Thank you! I found some other issues I might patch in future. :)