don't crash with possibly invalid index, fdo#76209
don't crash with possibly invalid index, fdo#76209

Change-Id: Idde31b2b07e27a1d9c91145516f8e78c638ce3b4

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