MDL-41185 fix url in course_viewed event after course deleted

Includes a minor fix for course invalidation after deleting of course,
this improvement should not affect normal execution, that is why
it was not backported.

lib/classes/event/course_viewed.php

@@ -70,14 +70,18 @@ class course_viewed extends \core\event\base {
     /**
      * Get URL related to the action.
      *
-     * @return \moodle_url
+     * @return \moodle_url|null
      */
     public function get_url() {
         $sectionid = null;
         if (isset($this->other['coursesectionid'])) {
             $sectionid = $this->other['coursesectionid'];
         }
-        return \course_get_url($this->courseid, $sectionid);
+        try {
+            return \course_get_url($this->courseid, $sectionid);
+        } catch (\Exception $e) {
+            return null;
+        }
     }
 
     /**

lib/moodlelib.php

@@ -4933,6 +4933,11 @@ function delete_course($courseorid, $showfeedback = true) {
     $DB->delete_records("course", array("id" => $courseid));
     $DB->delete_records("course_format_options", array("courseid" => $courseid));
 
+    // Reset all course related caches here.
+    if (class_exists('format_base', false)) {
+        format_base::reset_course_cache($courseid);
+    }
+
     // Trigger a course deleted event.
     $event = \core\event\course_deleted::create(array(
         'objectid' => $course->id,

lib/tests/events_test.php

@@ -245,14 +245,21 @@ class core_events_testcase extends advanced_testcase {
         // Trigger and capture the event.
         $sink = $this->redirectEvents();
         $event->trigger();
+        $loggeddata = $event->get_data();
         $events = $sink->get_events();
         $event = reset($events);
 
+
         $this->assertInstanceOf('\core\event\course_viewed', $event);
         $this->assertEquals(context_course::instance($course->id), $event->get_context());
         $expected = array($course->id, 'course', 'view section', 'view.php?id=' . $course->id . '&sectionid='
                 . $sectionid, $sectionid);
         $this->assertEventLegacyLogData($expected, $event);
         $this->assertEventContextNotUsed($event);
+
+        delete_course($course->id, false);
+        $restored = \core\event\base::restore($loggeddata, array('origin' => 'web', 'ip' => '127.0.0.1'));
+        $this->assertInstanceOf('\core\event\course_viewed', $restored);
+        $this->assertNull($restored->get_url());
     }
 }