fix crash on re-export of fdo64646-4.xls back to xls
fix crash on re-export of fdo64646-4.xls back to xls

Change-Id: Ic6d6e7d7d8d42af0fc739d964a1190d40f9dba2e

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core