plainfind_func: optimize for speed. plainfind_func: treat empty patterns as valid.
plainfind_func: optimize for speed.
plainfind_func: treat empty patterns as valid.

LuaDist/lrexlib-oniguruma,LuaDist/lrexlib-posix,LuaDist/lrexlib-tre,LuaDist/lrexlib-pcre,LuaDist/lrexlib-pcre,LuaDist/lrexlib-gnu,LuaDist/lrexlib-gnu,LuaDist/lrexlib-tre,StoneDot/lrexlib,StoneDot/lrexlib,LuaDist/lrexlib-posix,LuaDist/lrexlib-oniguruma