[skif] Simplify new input/output bounds recursion

Change-Id: I717a3053e181675fad36bec55f907885b998b5e2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/699217
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
13 files changed