fastparser: avoid std::stack::top() - cache it's results.
fastparser: avoid std::stack::top() - cache it's results.

amazingly std::stack::top() takes 146 pseudo-cycles to do not much,
so instead cache the result in a single pointer in lieu of burning
that code.

Change-Id: Ie326be47da6cbad0850e5f1026a1632bb840b6b8

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