If given a malformed LUKS header, it is possible that the algorithm
names end up being an empty string. This leads to confusing error
messages unless quoting is used to highlight where the empty string
is subsituted in the error message.

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>