delta-find: make sure we only use newer full snapshot as candidate
The current code does not needs to protect against this, as there are no older
snapshot in the current cache. However as we are getting ready to reuse this
cache from one revision to another, we need the code to protect itself about
what's coming.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}