Fix slicing for UnmaskedArrays (which come from Arrow).

[jpivarski]

No description provided.

[codecov]

Codecov Report

Merging #1499 (e34292f) into main (8a4ea2b) will increase coverage by 0.23%.
The diff coverage is 85.13%.

Impacted Files	Coverage Δ
src/awkward/_v2/contents/indexedarray.py	73.83% <ø> (ø)
src/awkward/_v2/operations/ak_cartesian.py	89.68% <ø> (ø)
src/awkward/_v2/operations/ak_full_like.py	100.00% <ø> (ø)
src/awkward/_v2/operations/ak_nan_to_none.py	26.66% <ø> (ø)
src/awkward/_v2/operations/ak_with_field.py	97.87% <ø> (ø)
src/awkward/_v2/contents/emptyarray.py	71.66% <50.00%> (-0.25%)	⬇️
src/awkward/_v2/contents/unmaskedarray.py	68.77% <50.00%> (-0.18%)	⬇️
src/awkward/_v2/_connect/jax/__init__.py	88.88% <66.66%> (-1.59%)	⬇️
src/awkward/_v2/operations/ak_from_avro_file.py	66.66% <66.66%> (ø)
src/awkward/_v2/_connect/jax/_reducers.py	76.92% <76.92%> (ø)
... and 33 more