MDL-49146 single-activity course format: key activity must be visible

With a single-activity course, visibility to students is controlled by
course visibility. There is no sense in having the key activity not
visible to students, and, if you did, the symptoms were almost
incomprehensible. It was very hard to work out what you had done wrong.

course/format/singleactivity/lib.php

@@ -230,8 +230,16 @@ class format_singleactivity extends format_base {
         }
 
         // Make sure the current activity is in the 0-section.
+        $changed = false;
         if ($activity && $activity->sectionnum != 0) {
             moveto_module($activity, $modinfo->get_section_info(0));
+            $changed = true;
+        }
+        if ($activity && !$activity->visible) {
+            set_coursemodule_visible($activity->id, 1);
+            $changed = true;
+        }
+        if ($changed) {
             // Cache was reset so get modinfo again.
             $modinfo = get_fast_modinfo($this->courseid);
         }