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

This eliminates 1 db query.

mod/wiki/prettyview.php

@@ -51,7 +51,7 @@ if (!$wiki = wiki_get_wiki($subwiki->wikiid)) {
     print_error('incorrectwikiid', 'wiki');
 }
 
-require_login($course->id, true, $cm);
+require_login($course, true, $cm);
 
 $context = get_context_instance(CONTEXT_MODULE, $cm->id);
 require_capability('mod/wiki:viewpage', $context);