hostnamectl: Exit with zero on success

In show_all_names(), bus_map_all_properties() returns 1 on success which is
then used as the return code of show_all_names() and eventually main(). Exit
with zero in main() on all nonnegative results to guard against similar errors.

src/hostname/hostnamectl.c

@@ -536,5 +536,5 @@ int main(int argc, char *argv[]) {
         r = hostnamectl_main(bus, argc, argv);
 
 finish:
-        return r < 0 ? EXIT_FAILURE : r;
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }