fix: include self._length in RegularArray.mergemany

[agoose77]

Fixes #1644

[codecov]

Codecov Report

Merging #1645 (f56041d) into main (9e17f29) will increase coverage by 0.46%.
The diff coverage is 63.67%.

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/_v2/_connect/cuda/__init__.py	0.00% <0.00%> (ø)
src/awkward/_v2/_connect/numexpr.py	88.40% <0.00%> (ø)
src/awkward/_v2/_connect/pyarrow.py	88.46% <0.00%> (ø)
...awkward/_v2/_connect/rdataframe/from_rdataframe.py	0.00% <0.00%> (ø)
...c/awkward/_v2/_connect/rdataframe/to_rdataframe.py	0.00% <0.00%> (ø)
src/awkward/_v2/_lookup.py	98.68% <ø> (+1.17%)	⬆️
src/awkward/_v2/numba.py	93.47% <0.00%> (ø)
src/awkward/_v2/operations/ak_from_avro_file.py	66.66% <0.00%> (ø)
src/awkward/_v2/operations/ak_local_index.py	100.00% <ø> (ø)
src/awkward/_v2/operations/ak_max.py	87.09% <ø> (ø)
... and 63 more

[jpivarski]

This is absolutely the right fix. (I just tried it out.)

I think the mistake was made when I was thinking that others is the full set of things to merge, forgetting that self should also be in that set?

[agoose77]

I think the mistake was made when I was thinking that others is the full set of things to merge, forgetting that self should also be in that set?

Yep, I think that's probably how it happened :)