message: style and nits for fee-checking in BroadcastTransaction
diff: #include <future>
  -static TransactionError HandleATMPError(const TxValidationState& state, std::string& err_string_out) {
  +static TransactionError HandleATMPError(const TxValidationState& state, std::string& err_string_out)
  +{
  err_string_out = state.ToString();
  if (state.IsInvalid()) {
  if (state.GetResult() == TxValidationResult::TX_MISSING_INPUTS) {
  @@ -50,10 +51,10 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
  if (!node.mempool->exists(hashTx)) {
  // Transaction is not already in the mempool.
  TxValidationState state;
  - CAmount fee{0};
  - if (max_tx_fee) {
  + if (max_tx_fee > 0) {
  // First, call ATMP with test_accept and check the fee. If ATMP
  // fails here, return error immediately.
  + CAmount fee{0};
  if (!AcceptToMemoryPool(*node.mempool, state, tx,
  false /* bypass_limits */)) {
  return HandleATMPError(state, err_string);
  