Fix an error message on docker-archive:path:name@sha256:$digest
Fix an error message on docker-archive:path:name@sha256:$digest

It's a possible user error, not a supposedly-unreachable internal
error.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/image,containers/image