tests/helper-killhook.py

rust-changelog: remove special parsing of empty changelog data for null rev

For the null revision, `Revlog::get_rev_data()` will return an empty
string (of bytes). We currently handle that case in
`ChangelogRevisionData::manifest_node()`. However, it's going to be
ugly to have special handling for the null revision for each future
method on `ChangelogRevisionData`. This patch therefore restructures
the code so we instead initialize the struct with valid data for the
null revision.

Differential Revision: https://phab.mercurial-scm.org/D12438

import os


def killme(ui, repo, hooktype, **wkargs):
    os._exit(80)