message: Fix accidental copy object
diff: @@ -150,7 +150,7 @@ CAmount SigmaSpendBuilder::GetChanges(std::vector<CTxOut>& outputs, CAmount amou
  sigma::DenominationToInteger(denomination, denominationValue);
  sigma::PrivateCoinV3 newCoin(params, denomination, ZEROCOIN_TX_VERSION_3);
  - sigma::PublicCoinV3 pubCoin = newCoin.getPublicCoin();
  + auto& pubCoin = newCoin.getPublicCoin();
  if (!pubCoin.validate()) {
  throw std::runtime_error("Unable to mint a V3 sigma coin.");
  