Add conditional to non attemp to create conservation certificate if response was empty

[xtornasol512]

RexChain/rexchain/blockchain/managers.py

Line 75 in 915e69c

xml_response = connector.generate_proof(new_block.merkleroot)

    xml_response = connector.generate_proof(new_block.merkleroot)
    new_block.data["xml_response"] = xml_response
    # Save
    new_block.save()
    # Save response on a  new table too

    certificate = ConservationCertificate(
        folio=xml_response["Folio"],
        raw_document=xml_response["Constancia"],
        reference=new_block.merkleroot
    )
    certificate.block = new_block
    certificate.data["xml_response"] = xml_response
    certificate.save()
    
This chunk of code must run only once, when the xml_response is not empty!