Merge #662: [0.17 backport] FundTransaction: mark all change keys as …

…kept #660

e50cbd7 FundTransaction: mark all change keys as kept (Gregory Sanders)

Pull request description:

  Backport of #660.

Tree-SHA512: 0fdeddc109c8f1f69b5a45c8a23171cebb68db7f21f7125a7769d28a3a7ed090602b28a1ec51b9a89a96becad07051b89951db1fef91fddc53f1f648099196da

src/wallet/wallet.cpp

@@ -2700,6 +2700,11 @@ bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nC
         }
     }
 
+    // Mark all un-returned change keys as used to reduce privacy loss
+    for (auto& changekey : vChangeKey) {
+        changekey->KeepKey();
+    }
+
     return true;
 }