pathops: Add missing header guards in two files.

Guards were missing in SkIntersectionHelper.h and
SkPathOpsTSect.h.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1914873002

Review URL: https://codereview.chromium.org/1914873002
2 files changed