check for navigator before testing userAgent. fixes #6037
check for navigator before testing userAgent. fixes #6037

arshaw/fullcalendar,arshaw/fullcalendar,fullcalendar/fullcalendar,fullcalendar/fullcalendar,oleg-babintsev/fullcalendar,fullcalendar/fullcalendar,arshaw/fullcalendar,oleg-babintsev/fullcalendar,oleg-babintsev/fullcalendar,arshaw/fullcalendar,fullcalendar/fullcalendar