ApproximateBestSubset should take inputs by reference, not value

src/wallet/wallet.cpp

@@ -2023,7 +2023,7 @@ void CWallet::AvailableCoins(std::vector<COutput>& vCoins, bool fOnlySafe, const
     }
 }
 
-static void ApproximateBestSubset(std::vector<std::pair<CAmount, std::pair<const CWalletTx*,unsigned int> > >vValue, const CAmount& nTotalLower, const CAmount& nTargetValue,
+static void ApproximateBestSubset(const std::vector<std::pair<CAmount, std::pair<const CWalletTx*,unsigned int> > >& vValue, const CAmount& nTotalLower, const CAmount& nTargetValue,
                                   std::vector<char>& vfBest, CAmount& nBest, int iterations = 1000)
 {
     std::vector<char> vfIncluded;