Only call data()/length() when self is valid()
Only call data()/length() when self is valid()

Change-Id: Icd9c12a10d2183a5159a3aa7a70e90494e8a8183

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