stack: fix phasecache._phasesets check logic
When _phasesets is not None, it's a list, and it contains set()s of revisions
in a specific phase, starting from public, draft, secret and so on. But since
repos are supposed to have the majority of revisions in public phase, the first
element of this list is not a (potentially huge) set, but None.
Previously this code tried to check if there's any element that is None, and
was always finding None at index 0, so the short path was executed every time
and the rest of the function was never used.
This software was downloaded from
https://www.mercurial-scm.org/repo/evolve/
Copyright 2011 Peter Arrenbrecht <peter.arrenbrecht@gmail.com>
Logilab SA <contact@logilab.fr>
Pierre-Yves David <pierre-yves.david@ens-lyon.org>
Patrick Mezard <patrick@mezard.eu>
This software may be used and distributed according to the terms of the GNU
General Public License version 2 or any later version.
On Debian systems, the complete text of the GNU General Public License version
2 can be found in `/usr/share/common-licenses/GPL-2'.