message: Do not select used zPiv on spend
diff: @@ -3930,9 +3930,10 @@ bool CWallet::CreateZerocoinSpendTransaction(libzerocoin::CoinDenomination denom
  // 1. Select a private coin not used in wallet
  LogPrintf("ZCPRINT %s step 1\n", __func__);
  + //todo add some sort of coin control style way to select which zerocoinmint to spend
  bool fSelected = false;
  for(const CZerocoinMint mint : listPubCoin) {
  - if(mint.GetDenominationAsInt() == denomination) {
  + if(mint.GetDenominationAsInt() == denomination && !mint.IsUsed()) {
  zerocoinSelected = mint;
  fSelected = true;
  }
  