histedit: use self.stateobj to check whether interrupted histedit exists
self.stateobj is an instance of state.cmdstate() class which has an .exists()
function which is used to check whether there exists an interrupted statefile or
not.
Differential Revision: https://phab.mercurial-scm.org/D3865
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}