fix requestJson reporting parse error when success handler failed
fix requestJson reporting parse error when success handler failed

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