mercurial/templates/json/changelist.tmpl

revlog: adapt the `reading` check for `unionrepo`

We cannot just rely on the length check for the `unionrepo` as the local revlog
might be empty while the other revlog contains data. In addition, we need to
also open the second revlog for reading when needed.

\{
  "node": {node|json},
  "changeset_count": {changesets|json},
  "changesets": [{join(entries%changelistentry, ", ")}]
}