New PartiallySignedTransaction constructor from CTransction

New constructor that creates a PartiallySignedTransaction from a
CTransaction, automatically sizing the inputs and outputs vectors for
convenience.

src/script/sign.cpp

@@ -513,6 +513,12 @@ bool IsSolvable(const SigningProvider& provider, const CScript& script)
     return false;
 }
 
+PartiallySignedTransaction::PartiallySignedTransaction(const CTransaction& tx) : tx(tx)
+{
+    inputs.resize(tx.vin.size());
+    outputs.resize(tx.vout.size());
+}
+
 bool PartiallySignedTransaction::IsNull() const
 {
     return !tx && inputs.empty() && outputs.empty() && unknown.empty();

src/script/sign.h

@@ -566,6 +566,7 @@ struct PartiallySignedTransaction
     bool IsSane() const;
     PartiallySignedTransaction() {}
     PartiallySignedTransaction(const PartiallySignedTransaction& psbt_in) : tx(psbt_in.tx), inputs(psbt_in.inputs), outputs(psbt_in.outputs), unknown(psbt_in.unknown) {}
+    explicit PartiallySignedTransaction(const CTransaction& tx);
 
     // Only checks if they refer to the same transaction
     friend bool operator==(const PartiallySignedTransaction& a, const PartiallySignedTransaction &b)

src/wallet/rpcwallet.cpp

@@ -3930,14 +3930,7 @@ UniValue walletcreatefundedpsbt(const JSONRPCRequest& request)
     FundTransaction(pwallet, rawTx, fee, change_position, request.params[3]);
 
     // Make a blank psbt
-    PartiallySignedTransaction psbtx;
-    psbtx.tx = rawTx;
-    for (unsigned int i = 0; i < rawTx.vin.size(); ++i) {
-        psbtx.inputs.push_back(PSBTInput());
-    }
-    for (unsigned int i = 0; i < rawTx.vout.size(); ++i) {
-        psbtx.outputs.push_back(PSBTOutput());
-    }
+    PartiallySignedTransaction psbtx(rawTx);
 
     // Fill transaction with out data but don't sign
     bool bip32derivs = request.params[4].isNull() ? false : request.params[4].get_bool();