changegroup: record changelogdone after fully consuming its data
Setting this as a side-effect of calling _close() is wonky. There's
only one group for changelog data. So we can wait until after all
data has been emitted before recording it.
Differential Revision: https://phab.mercurial-scm.org/D4136
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}