Fix: print() no output when used on hist() maps with large top args

[suyuee]

Currently, using print with a large top arg (any number larger than number
of map keys) on hist maps would result in a negative overflow bug, which will
make print fail to produce any output. This patch resolves this issue.

output.cpp
void TextOutput::map_hist
{
...
    if (top)
    {
        std::cerr << "values_by_key.size()       = " << values_by_key.size()       << std::endl;
        std::cerr << "                       top = " <<                        top << std::endl;
        std::cerr << "values_by_key.size() - top = " << values_by_key.size() - top << std::endl;
        if (i++ < (values_by_key.size() - top))
            continue;
    }
...
}

// output
# bpftrace -e 'kretprobe:vfs_read { @bytes = hist(retval); } i:s:5 {print(@bytes, 2, 1); exit();} END { clear(@bytes); }'
values_by_key.size()       = 1
                       top = 2
values_by_key.size() - top = 18446744073709551615

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md

[suyuee]

Update CHANGLOG.md

[danobi]

Nice, LGTM