revlog: simplify the try nesting in the `_writing` context
Lets use a single try, with conditional cleanup. This make is easier to add a
file handle dedicated to sidedata.
Differential Revision: https://phab.mercurial-scm.org/D10775
# mercurial.revlogutils -- basic utilities for revlog
#
# Copyright 2019 Pierre-Yves David <pierre-yves.david@octobus.net>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import