Handle non-invertible fits from linear or direct fit

Includes a three-entry table profile that produces a "direct" fit
result, but one that can't be inverted. The guarantees about
invertibility that we were asserting here only apply to profiles that go
through the nonlinear fit.

Bug: oss-fuzz:19341
Change-Id: Ia9597727e6787ac0e1345e3b93fd532a5d133919
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/259362
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
4 files changed