Finish adding schema updates to initial install function

booking.helper.inc

@@ -334,6 +334,12 @@ function _booking_max_dob_ts()
  */
 function _booking_avg_age($sum, $count, $reference_ts)
 {
+	//handle condition where count is zero
+	if ($count == 0)
+	{
+		return "Zero";
+	}
+	
 	global $event;
 	//calculate the average age timestamp
 	$average = $sum / $count;