fix StrictStringSort (and STL assertion in starmath test)
fix StrictStringSort (and STL assertion in starmath test)

OUString::compareTo may return not just -1 but any negative number.

(regression from 6a08067902ddc0ec61a7c7b4b0035b303f643a50)

Change-Id: I93027726b95e8d398292e1c2dee7795b1f7b7b8b

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