Fails if more device arguments are present for isLuks.

Fixes
http://code.google.com/p/cryptsetup/issues/detail?id=165

src/cryptsetup.c

@@ -1010,6 +1010,12 @@ static int action_isLuks(void)
 	struct crypt_device *cd = NULL;
 	int r;
 
+	/* FIXME: argc > max should be checked for other operations as well */
+	if (action_argc > 1) {
+		log_err(_("Only one device argument for isLuks operation is supported.\n"));
+		return -ENODEV;
+	}
+
 	if ((r = crypt_init(&cd, action_argv[0])))
 		goto out;