Use PrecomputedTransactionData in signet check

This is out of an abundance of caution only, as signet currently doesn't
enable taproot validation flags. Still, it seems cleaner to make sure
that all non-test code that passes MissingDataBehavior::ASSERT_FAIL
also actually makes sure no data can be missing.

src/signet.cpp

@@ -139,7 +139,9 @@ bool CheckSignetBlockSolution(const CBlock& block, const Consensus::Params& cons
     const CScript& scriptSig = signet_txs->m_to_sign.vin[0].scriptSig;
     const CScriptWitness& witness = signet_txs->m_to_sign.vin[0].scriptWitness;
 
-    TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /*nIn=*/ 0, /*amount=*/ signet_txs->m_to_spend.vout[0].nValue, MissingDataBehavior::ASSERT_FAIL);
+    PrecomputedTransactionData txdata;
+    txdata.Init(signet_txs->m_to_sign, {signet_txs->m_to_spend.vout[0]});
+    TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /*nIn=*/ 0, /*amount=*/ signet_txs->m_to_spend.vout[0].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
 
     if (!VerifyScript(scriptSig, signet_txs->m_to_spend.vout[0].scriptPubKey, &witness, BLOCK_SCRIPT_VERIFY_FLAGS, sigcheck)) {
         LogPrint(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution invalid)\n");