MDL-31607 use full course object for require_login() if already available

This eliminates 1 db query.

mod/wiki/lock.php

@@ -66,7 +66,7 @@ if (!empty($section) && !$sectioncontent = wiki_get_section_page($page, $section
     print_error('invalidsection', 'wiki');
 }
 
-require_login($course->id, false, $cm);
+require_login($course, false, $cm);
 
 $context = get_context_instance(CONTEXT_MODULE, $cm->id);
 require_capability('mod/wiki:editpage', $context);