message: rpc: Properly use underlying type in GetAllOutputTypes
  Don't blindly assume it is int.
  In practice this is usually `unsigned` or `int`, so this commit should
  not change behavior.
diff: @@ -504,7 +504,8 @@ static UniValue decoderawtransaction(const JSONRPCRequest& request)
  static std::string GetAllOutputTypes()
  {
  std::vector<std::string> ret;
  - for (int i = TX_NONSTANDARD; i <= TX_WITNESS_UNKNOWN; ++i) {
  + using U = std::underlying_type<txnouttype>::type;
  + for (U i = (U)TX_NONSTANDARD; i <= (U)TX_WITNESS_UNKNOWN; ++i) {
  ret.emplace_back(GetTxnOutputType(static_cast<txnouttype>(i)));
  }
  return Join(ret, ", ");
  