Booting a domain slave with no cached domain.xml and no available master does not exit as expected

As part of the empty config HC work, 0 length configurations were considered to be "empty". This is not correct in the case of domain.xml and a slave using --cached-dc if the master is unavailable on initial boot.

Since the embedded empty config is always using supressLoad with --empty-domain-config, zero length domain.xml / domain-cached.xml is an error, and result in an exception and exit.