Anonymous drupal users see 'undefined index' error when registering for event when certain non-essential permissions aren't enabled

If anonymous users haven't been given the 'view event info' AND 'view event participants' permissions, like 1619 of Activity.php generates an error and fails to create an activity record. The failure seems to stem from the fact that the event array created on line 1613 by getEvents() is empty, which is itself checkPermission() on line 319 of Event.php returns false.

I've attached my temporary patch, which should prevent the error in the meantime, but is not a long term solution.