reject non-3x3 gamut matrices

A fuzzer has produced one, and hit the existing 4x4 == 3x3 assert.

Bug: chromium:895763
Change-Id: Id24b982464166fe5b79ab26c1a3a0e931b76dc4c
Reviewed-on: https://skia-review.googlesource.com/c/163166
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed