message: Fix qt mint error message
diff: @@ -5912,7 +5912,7 @@ string CWallet::MintAndStoreZerocoin(vector<CRecipient> vecSend,
  LogPrintf("payTxFee.GetFeePerK()=%s\n", payTxFee.GetFeePerK());
  CReserveKey reservekey(this);
  - int64_t nFeeRequired;
  + int64_t nFeeRequired = 0;
  int nChangePosRet = -1;
  bool isSigmaMint = false;
  @@ -5985,7 +5985,7 @@ string CWallet::MintAndStoreZerocoinV3(vector<CRecipient> vecSend,
  LogPrintf("payTxFee.GetFeePerK()=%s\n", payTxFee.GetFeePerK());
  CReserveKey reservekey(this);
  - int64_t nFeeRequired;
  + int64_t nFeeRequired = 0;
  int nChangePosRet = -1;
  bool isSigmaMint = true;
  @@ -6056,7 +6056,7 @@ string CWallet::MintZerocoin(CScript pubCoin, int64_t nValue, bool isSigmaMint,
  return _("Insufficient funds");
  LogPrintf("payTxFee.GetFeePerK()=%s\n", payTxFee.GetFeePerK());
  CReserveKey reservekey(this);
  - int64_t nFeeRequired;
  + int64_t nFeeRequired = 0;
  if (IsLocked()) {
  string strError = _("Error: Wallet locked, unable to create transaction!");
  