MDL-73317 search: Close session later in script

The session write_close was moved to the earliest point in the script
that does not modify the session. This is currently always after
$OUTPUT->header()

search/index.php

@@ -48,9 +48,6 @@
     require_login();
 }
 
-// Unlock the session during a search.
-\core\session\manager::write_close();
-
 require_capability('moodle/search:query', $context);
 
 $searchrenderer = $PAGE->get_renderer('core_search');
@@ -169,6 +166,9 @@
 // We are ready to render.
 echo $OUTPUT->header();
 
+// Unlock the session only after outputting the header as this modifies the session cachestore.
+\core\session\manager::write_close();
+
 // Get the results.
 if ($data) {
     $results = $search->paged_search($data, $page);