Support creation of zero-sized primitive Java arrays

[niloc132]

Fixes #84

[devinrsmith]

Assuming pyBuffer is correct, there shouldn't be any way to trigger this. I wonder if we should prefer to remove the blocks

[niloc132]

Aside from trying to avoid creating zero-length arrays (which apparently work correctly, but perhaps it would be better to only keep references to singleton empty arrays?), I can't imagine why this check would have existed.

It isn't the only size < 0 check in the codebase, so it might still serve as a reasonable sanity check? I could easily go either way, will be guided by your preference.

[devinrsmith]

The majority of < 0 checks are against return values where -1 represents an exceptional state.

        itemCount = PySequence_Length(pyArg);
        if (itemCount < 0) {
            return -1;
        }

ie, this returns -1 if pyArg is not a sequence.

The one other extraneous check I could find is:

    *size = PyUnicode_GET_SIZE(pyUnicode);
    if (*size < 0) {
        goto error;
    }

I don't see any cpython documentation that this is expected to ever trigger - the assumption is that pyUnicode is a unicode object; and the code base does make that check.

As such, I think it makes sense to remove these exception checking blocks.