Correct choice in the case where CAC2 terminates without conflict

[hivenet-ludovicpaillat]

When CAC2 terminates without conflicts (i.e. processes agree on a single conflict-set), the choice of which message will be delivered must consider only messages that were delivered or for which we have a delivery proof. This is in order to maintain Agreement for Cascade Consensus.

distributed-mls/src/cascade_consensus.hpp

Lines 334 to 344 in bc7edc6

	std::vector<mls::MLSMessage> choices;
	for(const auto & ref : message.conflictingMessages)
	{
	if(!m_cacInstance1.messages().contains(ref))
	printf("CAC2 Deliver: Error unknown reference %u\n",
	MLS_UTIL_HASH_REF(ref));
	else
	choices.emplace_back(m_cacInstance1.messages().at(ref));
	}
	m_deliver(m_choice(choices));