fix: avoid fatal on get_segments

[leogermani]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Fixes an odd issue where this would break the sites in a combination of S3 Uploads and Newspack S3 Performance plugins...

See 1200550061930446-as-1203093685387025

How to test the changes in this Pull Request:

1. Smoke test

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

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[dkoo]

Weird bug, but good to be defensive in this situation!