Rework SwAutoFormat::IsBlanksInString
Rework SwAutoFormat::IsBlanksInString

The old code was convoluted and suffered the following issues:
* Relied on OUStrings being zero-terminated, which is not granted
* Systematically missed the end of string, accessing unrelated
  memory, in case there was just a single trailing space

Change-Id: I98dd0f94a8f48f40c467a02dfd01c7866266d9d4

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