wallet: Retrieve TXO directly in FetchSelectedInputs

Instead of searching mapWallet for the preselected inputs, search
m_txos.

wallet_fundrawtransaction.py spends external inputs and needs the change
output to also belong to the test wallet for the oversized tx test.

Author: achow101

src/wallet/spend.cpp

@@ -277,12 +277,8 @@ util::Result<PreSelectedInputs> FetchSelectedInputs(const CWallet& wallet, const
             input_bytes = GetVirtualTransactionSize(input_bytes, 0, 0);
         }
         CTxOut txout;
-        if (auto ptr_wtx = wallet.GetWalletTx(outpoint.hash)) {
-            // Clearly invalid input, fail
-            if (ptr_wtx->tx->vout.size() <= outpoint.n) {
-                return util::Error{strprintf(_("Invalid pre-selected input %s"), outpoint.ToString())};
-            }
-            txout = ptr_wtx->tx->vout.at(outpoint.n);
+        if (auto txo = wallet.GetTXO(outpoint)) {
+            txout = txo->GetTxOut();
             if (input_bytes == -1) {
                 input_bytes = CalculateMaximumSignedInputSize(txout, &wallet, &coin_control);
             }

src/wallet/wallet.cpp

@@ -4459,4 +4459,14 @@ void CWallet::RefreshAllTXOs()
         RefreshTXOsFromTx(wtx);
     }
 }
+
+std::optional<WalletTXO> CWallet::GetTXO(const COutPoint& outpoint) const
+{
+    AssertLockHeld(cs_wallet);
+    const auto& it = m_txos.find(outpoint);
+    if (it == m_txos.end()) {
+        return std::nullopt;
+    }
+    return it->second;
+}
 } // namespace wallet

src/wallet/wallet.h

@@ -524,6 +524,7 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
     std::set<Txid> GetTxConflicts(const CWalletTx& wtx) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
     const std::unordered_map<COutPoint, WalletTXO, SaltedOutpointHasher>& GetTXOs() const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet) { AssertLockHeld(cs_wallet); return m_txos; };
+    std::optional<WalletTXO> GetTXO(const COutPoint& outpoint) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
     /** Cache outputs that belong to the wallet from a single transaction */
     void RefreshTXOsFromTx(const CWalletTx& wtx) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);