MDL-46539 assign calendar: Fix lastcron value for assign cron

mod/assign/lib.php

@@ -896,6 +896,8 @@ function assign_cron() {
             $class::cron();
         }
     }
+
+    return true;
 }
 
 /**

mod/assign/locallib.php

@@ -1576,7 +1576,7 @@ class assign {
         // Only ever send a max of one days worth of updates.
         $yesterday = time() - (24 * 3600);
         $timenow   = time();
-        $lastcron = $DB->get_field('modules', 'lastcron', array('name'=>'mod_assign'));
+        $lastcron = $DB->get_field('modules', 'lastcron', array('name' => 'assign'));
 
         // Collect all submissions from the past 24 hours that require mailing.
         // Submissions are excluded if the assignment is hidden in the gradebook.