pull in roundtrip thresholds much more tightly

There are all sorts of dangerous values to work with up there near
INT_MAX, see associated bug.  We can just check we fall in the table.

Bug: oss-fuzz:8142
Change-Id: I3cc6844a6efbe5351d6714664faf39d3ded5bca7
Reviewed-on: https://skia-review.googlesource.com/125861
Auto-Submit: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed