[BugFix] instantiate DSA instance in TransactionVerifier

Author: Coding-Enthusiast

Src/Autarkysoft.Bitcoin/Blockchain/TransactionVerifier.cs

@@ -42,6 +42,7 @@ public TransactionVerifier(IConsensus consensus)
             this.consensus = consensus;
 
             calc = new Calc();
+            dsa = new DSA();
             scrSer = new ScriptSerializer();
             hash160 = new Ripemd160Sha256();
             sha256 = new Sha256();