MDL-33414: The setting $showviewlink needs to be passed by reference

This was preventing the view full submission/feedback link from appearing
everywhere in the assignment when the submission/feedback content had been
truncated in the summary because it was too long (or too many files)

mod/assign/assignmentplugin.php

@@ -344,7 +344,7 @@ abstract class assign_plugin {
      * @param bool $showviewlink Modifed to return whether or not to show a link to the full submission/feedback
      * @return string - return a string representation of the submission in full
      */
-    public function view_summary(stdClass $submissionorgrade, $showviewlink) {
+    public function view_summary(stdClass $submissionorgrade, & $showviewlink) {
         return '';
     }