This was being set to zero instead of one by mistake. Interestingly,
this was undetected by the CPU backend, but appears to matter sometimes
on the GPU side.
Change-Id: If827863f69c140f933696c6ff55c8a7095620c29
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368858
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>