robustify SkScaleToSides::AdjustRadii()

The fuzzer has a found a pathological case where the maxRadius
needs to be reduce by 17 ulps.

Reduce the larger radius an ulp at a time until the sum fits.

Change-Id: I9cc4528667e7f9e902eff34d447fd4040a09742e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309417
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
3 files changed