MDL-48493 admin: Fix PHP warning thrown if unable to detect component
MDL-48493 admin: Fix PHP warning thrown if unable to detect component

The method detect_plugin_component() returns false or string. The
normalize_component() expects strings only. Passing false to it
(typically when the plugin does not declare its component) caused the
PHP warning.

Credit goes to Ankit Agarwal for spotting this during testing.

dilawar/moodle