Fix creation of empty sequence on CertificatePolicies Extension

[ghm12]

Currently, when creating a Certificate which has the Certificate Policies extension but the included policy has no Policy Qualifier, the certificate is issued with an empty qualifiers sequence. According to RFC 5280 the policyQualifiers is an optional field, however if it exists it must be greater than zero, and thus the empty sequence would make the Certificate format invalid.

   PolicyInformation ::= SEQUENCE {
        policyIdentifier   CertPolicyId,
        policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                                PolicyQualifierInfo OPTIONAL } 

To fix this, before creating the policyQualifiers sequence, first it checks if said Policy has any qualifiers and only creates the sequence if it does.