\external_settings::__construct checks for "defined" variables which are always defined

On Master

1. Turn on autolink filter for all content and heading.
2. Go to a course and edit coursename. Something like this -

   <span class="multilang" lang="en">your_content_in English</span>

   <span class="multilang" lang="ar">your_content_in_arabic_here</span>

3. Go to your dashboard and make sure when you switch languages between English and Arabic, correct content is shown in courses summary tab.

On all branches

1. Run all test suites (behat + phpunit), this patch can possibly expose other existing bugs.
2. Create a file called test.php with content -

   define('AJAX_SCRIPT', true);

   require_once(__DIR__ . '/config.php');

   require_once("lib/externallib.php");

   $settings = external_settings::get_instance();

   print_object((int)$settings->get_filter());

3. Load it on browser and see the value should be 0
4. Create another file with code -

   require_once(__DIR__ . '/config.php');

   require_once("lib/externallib.php");

   $settings = external_settings::get_instance();

   print_object((int)$settings->get_filter());

5. Load it and check value, should be 1