[Wallet] unset change position when there is no change on exact match

qa/rpc-tests/fundrawtransaction.py

@@ -54,6 +54,11 @@ class RawTransactionsTest(BitcoinTestFramework):
         self.nodes[0].generate(121)
         self.sync_all()
 
+        # ensure that setting changePosition in fundraw with an exact match is handled properly
+        rawmatch = self.nodes[2].createrawtransaction([], {self.nodes[2].getnewaddress():50})
+        rawmatch = self.nodes[2].fundrawtransaction(rawmatch, {"changePosition":1, "subtractFeeFromOutputs":[0]})
+        assert_equal(rawmatch["changepos"], -1)
+
         watchonly_address = self.nodes[0].getnewaddress()
         watchonly_pubkey = self.nodes[0].validateaddress(watchonly_address)["pubkey"]
         watchonly_amount = Decimal(200)

src/wallet/wallet.cpp

@@ -2587,9 +2587,10 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                         vector<CTxOut>::iterator position = txNew.vout.begin()+nChangePosInOut;
                         txNew.vout.insert(position, newTxOut);
                     }
-                }
-                else
+                } else {
                     reservekey.ReturnKey();
+                    nChangePosInOut = -1;
+                }
 
                 // Fill vin
                 //