Boris Feld <boris.feld@octobus.net> [Thu, 15 Jun 2017 20:40:07 +0200] rev 2592
compat: make obshistory._getdifflines compatible with mercurial 4.1
On Mercurial version 4.1 and lower, patch.diff seems to returns an empty list
when there is no change. Mercurial 4.2 returns None so we add a if for this
case.