Add ContainsTransaction Recheck when ParallelVerifiedTransaction Rece…

…ived (#1408)

* add containsTx recheck

* add UT

* Update to just View check

* update

* revert

* Update UT_Blockchain.cs

Co-authored-by: Vitor Nazário Coelho <vncoelho@gmail.com>

src/neo/Ledger/Blockchain.cs

@@ -429,7 +429,9 @@ private void OnParallelVerified(ParallelVerified parallelVerified)
             RelayResultReason reason = parallelVerified.VerifyResult;
             if (reason == RelayResultReason.Succeed)
             {
-                if (!MemPool.CanTransactionFitInPool(parallelVerified.Transaction))
+                if (View.ContainsTransaction(parallelVerified.Transaction.Hash))
+                    reason = RelayResultReason.AlreadyExists;
+                else if (!MemPool.CanTransactionFitInPool(parallelVerified.Transaction))
                     reason = RelayResultReason.OutOfMemory;
                 else if (!MemPool.TryAdd(parallelVerified.Transaction.Hash, parallelVerified.Transaction))
                     reason = RelayResultReason.OutOfMemory;