consensus: misc fixes (#276)

* fix decoy checks + fee calculation

* fmt

consensus/src/transactions.rs

@@ -393,6 +393,11 @@ async fn verify_transactions_decoy_info<D>(
 where
     D: Database + Clone + Sync + Send + 'static,
 {
+    // Decoy info is not validated for V1 txs.
+    if hf == HardFork::V1 || txs.is_empty() {
+        return Ok(());
+    }
+
     batch_get_decoy_info(&txs, hf, database)
         .await?
         .try_for_each(|decoy_info| decoy_info.and_then(|di| Ok(check_decoy_info(&di, &hf)?)))?;

consensus/src/transactions/free.rs

@@ -78,7 +78,8 @@ pub fn tx_fee(tx: &Transaction) -> Result<u64, TransactionError> {
             }
 
             for output in &prefix.outputs {
-                fee.checked_sub(output.amount.unwrap_or(0))
+                fee = fee
+                    .checked_sub(output.amount.unwrap_or(0))
                     .ok_or(TransactionError::OutputsTooHigh)?;
             }
         }