MINIFICPP-739: Resolve json checks for c2 responses

[phrocker]

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[arpadboda]

Ouch. It's pretty painful that both can occur.

I my opinion the following way is a bit more straight forward to deal with this, but I don't adhere to it:

std::array<std::string, 2> ops = {"requested_operations", "requestedOperations"};
auto it = ops.begin();
for(; it != ops.end() ; ++it) {
  if(root.HasMember(*it) && root[*it].Size() > 0) break;
}
if(it == ops.end()) //none found 
  return C2Payload(payload.getOperation(), state::UpdateState::READ_COMPLETE, true);

//no need to bother with size as it's surely found
for (const rapidjson::Value& request : root[*it].GetArray()) {
...

[apiri]

reviewing