Ensure that ArithmeticFPInputs is fully initialized

Change-Id: Ia5e94704955aba33e07592711656fbeefef15912
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268840
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed