bumpfee: Clear scriptSigs and scriptWitnesses before calculated max size

The max size calculation expects some inputs to have empty scriptSigs
and witnesses, so we need to clear these before doing that calculation.

Author: achow101

src/wallet/feebumper.cpp

@@ -242,7 +242,13 @@ Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCo
     if (coin_control.m_feerate) {
         // The user provided a feeRate argument.
         // We calculate this here to avoid compiler warning on the cs_wallet lock
-        const int64_t maxTxSize{CalculateMaximumSignedTxSize(*wtx.tx, &wallet, &new_coin_control).vsize};
+        // We need to make a temporary transaction with no input witnesses as the dummy signer expects them to be empty for external inputs
+        CMutableTransaction mtx{*wtx.tx};
+        for (auto& txin : mtx.vin) {
+            txin.scriptSig.clear();
+            txin.scriptWitness.SetNull();
+        }
+        const int64_t maxTxSize{CalculateMaximumSignedTxSize(CTransaction(mtx), &wallet, &new_coin_control).vsize};
         Result res = CheckFeeRate(wallet, wtx, *new_coin_control.m_feerate, maxTxSize, old_fee, errors);
         if (res != Result::OK) {
             return res;