fix: only check length against empty form in ak.from_buffers if it is known

[ikrommyd]

We cannot check if the length is zero in the case of EmptyForm if the recursion earlier set it to unknown length. We skip the check in that case.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.72%. Comparing base (b749e49) to head (f635363).
⚠️ Report is 464 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/operations/ak_from_buffers.py	94.47% <100.00%> (+0.35%)	⬆️

... and 199 files with indirect coverage changes

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[ariostas]

This indeed fixes my issues in Uproot

[github-actions]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR3714

[ikrommyd]

This indeed fixes my issues in Uproot

This is naturally skipping a "validity check" that's impossible in this scenario but that's always the case for virtual arrays. You need to assume during array creation that the buffers that are passed in are correct. So the responsibility falls on the person passing the buffers, but that's the best we can do since we cannot look at the data at the from buffers stage.

[ianna]

@ikrommyd - great, thanks for fixing it! Please merge it if you are done with it. Thanks.