fixed xml parsing issue with singleton formula
fixed xml parsing issue with singleton formula

SheetJS/js-xlsx,iCasa/js-xlsx,iCasa/js-xlsx,SheetJS/js-xlsx,kaktus40/js-xlsx,kaktus40/js-xlsx,kaktus40/js-xlsx,thien-thach/searchFromExcel,iCasa/js-xlsx,kaktus40/js-xlsx,thien-thach/searchFromExcel,SheetJS/js-xlsx,iCasa/js-xlsx,SheetJS/js-xlsx