.arcconfig

bundle: do not detect --base argument that match nothing as lack of argument

With the previous version of the code, if --base did not match anything, it will
be handled as if no --base was provided and will fallback to using discovery
with the default path. This has two issues :
- The resulting bundle won't match what the user requested,
- if not default path is configured, it will crash.

We now properly distinct between the two cases and if the --base query does not
find any changeset, we will assume that everything under --rev needs to be sent.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}