core: fix DutyFlag check in GetScriptHashesForVerifying()

It's a flag (used by Share and Invoice asset types), so it should be checked
like a flag, the same way C# node does.

pkg/core/blockchain.go

@@ -899,7 +899,7 @@ func (bc *Blockchain) GetScriptHashesForVerifying(t *transaction.Transaction) ([
 		if as == nil {
 			return nil, errors.New("Invalid operation")
 		}
-		if as.AssetType == transaction.DutyFlag {
+		if as.AssetType&transaction.DutyFlag != 0 {
 			for _, o := range outputs {
 				h := o.ScriptHash
 				if _, ok := hashes[h]; !ok {