[#XX] client: Terminate session in ReadIteratorItems

* Make an invoker terminate session by its ID before return, otherwise,
  it may lead to `max session capacity reached error`.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

commonclient/iterator.go

@@ -29,6 +29,10 @@ func ReadIteratorItems(inv Invoker, batchSize int, contract util.Uint160, method
 		return arr, nil
 	}
 
+	defer func() {
+		_ = inv.TerminateSession(sessionID)
+	}()
+
 	var shouldStop bool
 	res := arr
 	for !shouldStop {