Revisit some illogical code from #183

[stronk7]

Form @ewallah, in recently fixed #179 (PR #183):

The loadCoreComponent function has to fail if dirroot is not set. First a new empty class is created, the next step evaluates the dirroot of this (empty) class. (/codechecker/moodle/Util/MoodleUtil.php)

if (!isset($CFG->dirroot)) { // No defined, let's start from scratch.
        $CFG = new \stdClass();
}
if ($CFG->dirroot !== $moodleRoot) { // Different, set the minimum required.

We need to revisit that "illogical" code (just noting that, normally it uses to be set, but should work if not, too).

Thanks for the report!

Ciao :-)