Add missing check in h_do_parse() for parser->vtable->higher in packrat.c

In packrat.c, there is a check for parser->vtable->higher at the start of the function, h_do_parser(), to avoid recall on lower level functions, however there is a missing check to not cache lower level functions when parsing input further down the function. This affects cache performance.

I cherry-picked this into hammer/hammer; in the future please make merge requests against the canonical Hammer repo.

closed