handle 'surt_ordered: False'

[ranafayed]

Description

Motivation and Context

Screenshots (if appropriate):

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.

[ikreymer]

Thanks for the PR!
This is not a common use case, but good to have it supported for your workflow!

It looks like the tests are failing with this change so far: https://travis-ci.com/github/webrecorder/pywb/jobs/400118397
Could you take a look, and perhaps also add a test for surt_ordered: false with a small cdx?

Let me know if you have any questions.