fixed assertion error when calling matrixCompMult()

Change-Id: I8e702eededf150e82226477558118f1bb7e66fef
Reviewed-on: https://skia-review.googlesource.com/8138
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed