turn on -fsanitize=integer on portable bot

There's one place where we're harmlessly underflowing
a U32, the not-taken side of an if_then_else().  Rather
than do something awkward to work around it, just stifle.

Change-Id: Ifb983cffb6c2a6c9281f5ec0bc0d67021bf82741
Reviewed-on: https://skia-review.googlesource.com/144622
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed