migration: Fix early failure cleanup

Avoid crash in cleanup after a very early migration failure
(possibly due to my 688a3dcba980bf01344a  'Route errors down ...')

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20180212160340.15333-2-dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
1 file changed