External input fund support cleanups

Synchronize error checking for external inputs
Rename external output Select to SelectExternal
Const FundTransaction variables

src/wallet/coincontrol.h

@@ -93,7 +93,7 @@ public:
         setSelected.insert(output);
     }
 
-    void Select(const COutPoint& outpoint, const CTxOut& txout)
+    void SelectExternal(const COutPoint& outpoint, const CTxOut& txout)
     {
         setSelected.insert(outpoint);
         m_external_txouts.emplace(outpoint, txout);

src/wallet/rpcwallet.cpp

@@ -3292,7 +3292,7 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
     }
 
     if (options.exists("solving_data")) {
-        UniValue solving_data = options["solving_data"].get_obj();
+        const UniValue solving_data = options["solving_data"].get_obj();
         if (solving_data.exists("pubkeys")) {
             for (const UniValue& pk_univ : solving_data["pubkeys"].get_array().getValues()) {
                 const std::string& pk_str = pk_univ.get_str();
@@ -3300,7 +3300,7 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
                     throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("'%s' is not hex", pk_str));
                 }
                 const std::vector<unsigned char> data(ParseHex(pk_str));
-                CPubKey pubkey(data.begin(), data.end());
+                const CPubKey pubkey(data.begin(), data.end());
                 if (!pubkey.IsFullyValid()) {
                     throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("'%s' is not a valid public key", pk_str));
                 }
@@ -3365,7 +3365,7 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
     wallet.chain().findCoins(coins);
     for (const auto& coin : coins) {
         if (!coin.second.out.IsNull()) {
-            coinControl.Select(coin.first, coin.second.out);
+            coinControl.SelectExternal(coin.first, coin.second.out);
         }
     }
 

src/wallet/spend.cpp

@@ -475,7 +475,7 @@ bool SelectCoins(const CWallet& wallet, const std::vector<COutput>& vAvailableCo
 
         CInputCoin coin(outpoint, txout, input_bytes);
         nValueFromPresetInputs += coin.txout.nValue;
-        if (coin.m_input_bytes <= 0) {
+        if (coin.m_input_bytes == -1) {
             return false; // Not solvable, can't estimate size for fee
         }
         coin.effective_value = coin.txout.nValue - coin_selection_params.m_effective_feerate.GetFee(coin.m_input_bytes);
@@ -814,7 +814,7 @@ static bool CreateTransactionInternal(
     // Calculate the transaction fee
     TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
     int nBytes = tx_sizes.vsize;
-    if (nBytes < 0) {
+    if (nBytes == -1) {
         error = _("Missing solving data for estimating transaction size");
         return false;
     }