psbt: Make sighash_type std::optional<int>

It is better to ues an optional to determine whether the sighash type
is set rather than using 0 as a magic number.

Author: achow101

src/psbt.h

@@ -57,7 +57,7 @@ struct PSBTInput
     std::map<CPubKey, KeyOriginInfo> hd_keypaths;
     std::map<CKeyID, SigPair> partial_sigs;
     std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
-    int sighash_type = 0;
+    std::optional<int> sighash_type;
 
     bool IsNull() const;
     void FillSignatureData(SignatureData& sigdata) const;
@@ -86,9 +86,9 @@ struct PSBTInput
             }
 
             // Write the sighash type
-            if (sighash_type > 0) {
+            if (sighash_type != std::nullopt) {
                 SerializeToVector(s, PSBT_IN_SIGHASH);
-                SerializeToVector(s, sighash_type);
+                SerializeToVector(s, *sighash_type);
             }
 
             // Write the redeem script
@@ -201,7 +201,9 @@ struct PSBTInput
                     } else if (key.size() != 1) {
                         throw std::ios_base::failure("Sighash type key is more than one byte type");
                     }
-                    UnserializeFromVector(s, sighash_type);
+                    int sighash;
+                    UnserializeFromVector(s, sighash);
+                    sighash_type = sighash;
                     break;
                 case PSBT_IN_REDEEMSCRIPT:
                 {

src/rpc/rawtransaction.cpp

@@ -1255,8 +1255,8 @@ static RPCHelpMan decodepsbt()
         }
 
         // Sighash
-        if (input.sighash_type > 0) {
-            in.pushKV("sighash", SighashToStr((unsigned char)input.sighash_type));
+        if (input.sighash_type != std::nullopt) {
+            in.pushKV("sighash", SighashToStr((unsigned char)*input.sighash_type));
         }
 
         // Redeem script and witness script

src/wallet/scriptpubkeyman.cpp

@@ -633,7 +633,7 @@ TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psb
         }
 
         // Get the Sighash type
-        if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
+        if (sign && input.sighash_type != std::nullopt && *input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
         }
 
@@ -2114,7 +2114,7 @@ TransactionError DescriptorScriptPubKeyMan::FillPSBT(PartiallySignedTransaction&
         }
 
         // Get the Sighash type
-        if (sign && input.sighash_type > 0 && input.sighash_type != sighash_type) {
+        if (sign && input.sighash_type != std::nullopt && *input.sighash_type != sighash_type) {
             return TransactionError::SIGHASH_MISMATCH;
         }