Don't fail if a candidate certificate has no SANs

Don't fail if a candidate certificate has no SANs

When we're doing certificate matching and we're asked for the list of
SAN values for a certifiate, and it contains none, don't return an
error, as that will eventually cause the module to just return an error.
Instead, just return an empty list of SAN values so that processing will
continue on to check if other certificates match.