use empty instead of size to check if vector is empty
use empty instead of size to check if vector is empty

Change-Id: I6c90b95bdf2de441594d5d5c36f76e6aeeb74011

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