more casts to make old GCC happy

    ... plus, a bot that uses said old GCC!

Change-Id: Idd242ece4a1a2e02af53faf5637bdaf696957349
Reviewed-on: https://skia-review.googlesource.com/99863
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
3 files changed