ak.argmax doesn't produce correct result for inner axis with nonzero start

[agoose77]

Version of Awkward Array

1.4.0

Description and code to reproduce

This is possibly related to #998 , but I wanted to open a new issue in case it is not.

Given this reproducer, the result loses certain elements

import awkward as ak
import numpy as np

array = ak.Array(
    ak.layout.ListOffsetArray64(
        ak.layout.Index64(np.r_[1, 3, 5]),
        ak.layout.ListOffsetArray64(
            ak.layout.Index64(np.r_[0, 3, 5, 8, 10, 12]),
            ak.layout.NumpyArray(
                np.r_[
                    1.8125,###
                    0.81252,###
                    -0.937,###

                    6.0,
                    -0.6875,

                    1.3125,
                    21.3125,
                    4.0,

                    9.8,
                    2.2,

                    33.0,
                    44.6,
                ]
            ),
        )
    )
)
assert ak.to_list(ak.argmax(array, axis=1)) == [[0, 1, 1], [1, 1]]

[jpivarski]

Issue 1000! 🎉

I'll be looking at the issues and PRs associated with nonzero starts soon. It's probably related to the code I was looking at last night.