Use HandleMissingData also in CheckSchnorrSignature

src/script/interpreter.cpp

@@ -1711,7 +1711,7 @@ bool GenericTransactionSignatureChecker<T>::CheckSchnorrSignature(Span<const uns
         if (hashtype == SIGHASH_DEFAULT) return set_error(serror, SCRIPT_ERR_SCHNORR_SIG_HASHTYPE);
     }
     uint256 sighash;
-    assert(this->txdata);
+    if (!this->txdata) return HandleMissingData(m_mdb);
     if (!SignatureHashSchnorr(sighash, execdata, *txTo, nIn, hashtype, sigversion, *this->txdata, m_mdb)) {
         return set_error(serror, SCRIPT_ERR_SCHNORR_SIG_HASHTYPE);
     }