Fix MSVC warnings about possible value truncation.

Patch from Peter Kasting <pkasting@chromium.org>

BUG=81439
TEST=none
Review URL:https://codereview.chromium.org/512923003/

Conflicts:
	src/cff.cc
	src/gasp.cc
	src/kern.cc
	src/loca.cc
	src/ltsh.cc
	src/name.cc
	src/ots.cc
	src/post.cc
	src/vorg.cc
	src/woff2.cc
Follow up previous commit