psbt: refactor version checks to use future-proof patterns

Author: TechLateef

btcutil/psbt/updater.go

@@ -110,20 +110,18 @@ func (u *Updater) addPartialSignature(inIndex int, sig []byte,
 
 	// Next, we perform a series of additional sanity checks.
 	if pInput.NonWitnessUtxo != nil {
-		var numInputs int
-		if u.Upsbt.Version == 2 {
-			numInputs = len(u.Upsbt.Inputs)
-		} else {
+		numInputs := len(u.Upsbt.Inputs)
+		if u.Upsbt.Version < 2 {
 			numInputs = len(u.Upsbt.UnsignedTx.TxIn)
 		}
+
 		if numInputs < inIndex+1 {
 			return ErrInvalidPrevOutNonWitnessTransaction
 		}
 
 		var prevHash chainhash.Hash
-		if u.Upsbt.Version == 2 {
-			copy(prevHash[:], pInput.PreviousTxid)
-		} else {
+		copy(prevHash[:], pInput.PreviousTxid)
+		if u.Upsbt.Version < 2 {
 			prevHash = u.Upsbt.UnsignedTx.TxIn[inIndex].PreviousOutPoint.Hash
 		}
 		if pInput.NonWitnessUtxo.TxHash() != prevHash {
@@ -135,10 +133,9 @@ func (u *Updater) addPartialSignature(inIndex int, sig []byte,
 		// that with the P2SH scriptPubKey that is generated by
 		// redeemScript.
 		if pInput.RedeemScript != nil {
-			var outIndex uint32
-			if u.Upsbt.Version == 2 {
-				outIndex = pInput.OutputIndex
-			} else {
+
+			outIndex := pInput.OutputIndex
+			if u.Upsbt.Version < 2 {
 				outIndex = u.Upsbt.UnsignedTx.TxIn[inIndex].PreviousOutPoint.Index
 			}
 			scriptPubKey := pInput.NonWitnessUtxo.TxOut[outIndex].PkScript