don't call top on an empty stack
don't call top on an empty stack

Change-Id: Ibe4b4d3785535816b40d46fd0baa60f01e1f9d33

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