CRM-5352 civicrm_activities_get_contact() returns "Invalid Data" error when no activities exist for contact

civicrm_activities_get_contact() returns "Invalid Data" error when no activities exist for contact.

The function hasn't failed, so it should not return an error. It should return an empty array of activities.

$activity = array('contact_id' => $objectId);
$ret = civicrm_activities_get_contact($activity);