Set return code to 0 on proper --help

Change-Id: Ic1b60bec6b85209040d4a270e45aa3f6e8f64e51

src/knot/main.c

@@ -120,6 +120,9 @@ int main(int argc, char **argv)
 			return 0;
 		case 'h':
 		case '?':
+			free(config_fn);
+			help(argc, argv);
+			return 0;
 		default:
 			free(config_fn);
 			help(argc, argv);