psbt: Use specified sighash or SIGHASH_DEFAULT when dummy signing

When dummy signing for finalizing, use either the specificed sighash, or
SIGHASH_DEFAULT, rather than always SIGHASH_ALL.

For outputs, just use SIGHASH_DEFAULT.

src/psbt.cpp

@@ -368,7 +368,7 @@ void UpdatePSBTOutput(const SigningProvider& provider, PartiallySignedTransactio
     // Construct a would-be spend of this output, to update sigdata with.
     // Note that ProduceSignature is used to fill in metadata (not actual signatures),
     // so provider does not need to provide any private keys (it can be a HidingSigningProvider).
-    MutableTransactionSignatureCreator creator(tx, /*input_idx=*/0, out.nValue, SIGHASH_ALL);
+    MutableTransactionSignatureCreator creator(tx, /*input_idx=*/0, out.nValue, SIGHASH_DEFAULT);
     ProduceSignature(provider, creator, out.scriptPubKey, sigdata);
 
     // Put redeem_script, witness_script, key paths, into PSBTOutput.
@@ -506,7 +506,8 @@ bool FinalizePSBT(PartiallySignedTransaction& psbtx)
     bool complete = true;
     const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
     for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
-        complete &= SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, &txdata, SIGHASH_ALL, nullptr, true);
+        int sighash_type = psbtx.inputs.at(i).sighash_type.value_or(SIGHASH_DEFAULT);
+        complete &= SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, &txdata, sighash_type, nullptr, true);
     }
 
     return complete;