allow repos to be created when only config entries present

specifically, 16f2d9b doesn't cut it.  That only works when you migrated a
whole bunch of repos from elsewhere, gave them all access using @all or some
pattern, then give individual config lines to each.

In this case the repo doesn't even exist, so the same logic (of treating
config lines as equivalent to rule lines) must extend to the *creation* of a
repo.