fix access to potentiellement empty string
fix access to potentiellement empty string

Change-Id: I84fc6b7e5528b677411163ee3c9d05d4f2e6feb2

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