tst: contrib malware mapping: fix argument parsing test

the old code assumed that there were no command line arguments to the
calling program.
now set the arguments explicitly to []

contrib/malware_name_mapping/test_download_mapping.py

@@ -89,7 +89,7 @@ def test_parser_default_argument(self):
 
     def test_parser_no_default(self):
         parser = create_parser()
-        args = parser.parse_args()
+        args = parser.parse_args([])
         self.assertEqual(args.add_default, None)