crypto: assert cipher algorithm is always valid

Crypto routines 'qcrypto_cipher_get_block_len' and
'qcrypto_cipher_get_key_len' return non-zero cipher block and key
lengths from static arrays 'alg_block_len[]' and 'alg_key_len[]'
respectively. Returning 'zero(0)' value from either of them would
likely lead to an error condition.

Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
