MDL-44536 workshop: Instantiate with the plain course module record

When the workshop class constructor signature was designed, the class
cm_info did not exist yet. Instead, plain course modules records were
used everywhere - including the $mod parameter in the
workshop_user_complete() callback. Even if cm_info is backwards
compatible with the plain data record when it comes to behaviour, it
must not be passed where the workshop API expects the stdClass (coding
error is thrown).

Alternative solution would be to remove the type hinting in the workshop
constructor. That is what the 'assign' class does, for example (the
inline docs describe the expected type to be stdClass, but that is not
forced via the method declaration).

As the problem seems to be pretty sole, I prefer not touching the
workshop internal API for now. So we let the cm_info degrade back into
the stdClass to make the workshop constructor happy without significant
performance lost.

mod/workshop/lib.php

@@ -301,6 +301,12 @@ function workshop_user_complete($course, $user, $mod, $workshop) {
     require_once(dirname(__FILE__).'/locallib.php');
     require_once($CFG->libdir.'/gradelib.php');
 
+    if ($mod instanceof cm_info) {
+        // We need to degrade here as the {@link workshop} class constructor
+        // expects the plain course module record.
+        $mod = $mod->get_course_module_record();
+    }
+
     $workshop   = new workshop($workshop, $mod, $course);
     $grades     = grade_get_grades($course->id, 'mod', 'workshop', $workshop->id, $user->id);