sshpeer: fix path when handling invalid url exception
In
73ed1d13c0bf the code was refactored but the error handling seems to have
been missed (or maybe the object shoud have implemented __bytes__)
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}