vcl: protect against out-of-bound access of empty OUString
vcl: protect against out-of-bound access of empty OUString

Change-Id: If2671ba0547eb69fce7005f5427dcd175a5c29a2

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