Fix a couple of issues with PS fee calculations (#3077)

* Fix PS fee calculations in GUI

Fixes the GUI fee estimation in Coin Control dialog when creating PS txes with the fSubtractFeeFromAmount option.

* Add missing nChangePosInOut reset for PS txes

Author: UdjinM6

src/qt/coincontroldialog.cpp

@@ -554,15 +554,18 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
         if (nPayAmount > 0)
         {
             nChange = nAmount - nPayAmount;
-            if (!CoinControlDialog::fSubtractFeeFromAmount)
-                nChange -= nPayFee;
 
             // PrivateSend Fee = overpay
             if(coinControl->fUsePrivateSend && nChange > 0)
             {
-                nPayFee += nChange;
+                nPayFee = std::max(nChange, nPayFee);
                 nChange = 0;
+                if (CoinControlDialog::fSubtractFeeFromAmount)
+                    nBytes -= 34; // we didn't detect lack of change above
+            } else if (!CoinControlDialog::fSubtractFeeFromAmount) {
+                nChange -= nPayFee;
             }
+
             // Never create dust outputs; if we would, just add the dust to the fee.
             if (nChange > 0 && nChange < MIN_CHANGE)
             {

src/wallet/wallet.cpp

@@ -3782,6 +3782,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                 {
                     //over pay for denominated transactions
                     if (nCoinType == ONLY_DENOMINATED) {
+                        nChangePosInOut = -1;
                         nFeeRet += nChange;
                         wtxNew.mapValue["DS"] = "1";
                     } else {