MDL-36424 wiki: set group so subwiki tabs/pages display correctly

mod/wiki/view.php

@@ -177,6 +177,10 @@ if ($id) {
 
     $groupmode = groups_get_activity_groupmode($cm);
 
+    // This is where people will land when they change groups using the drop-down selector.
+    // Set the activity group so tabs and content are shown correctly.
+    $currentgroup = groups_get_activity_group($cm, true);
+
     if ($wiki->wikimode == 'individual' && ($groupmode == SEPARATEGROUPS || $groupmode == VISIBLEGROUPS)) {
         list($gid, $uid) = explode('-', $groupanduser);
     } else if ($wiki->wikimode == 'individual') {