Avoid potential for division by zero in sk_clamp_grad_4.

Based on the structure of the checks, there's no way to enter an if
block if the denominator of the division would be zero.

Change-Id: I252c05aab43f26984afa2eab89648d5ec4e280b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/541074
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: James Godfrey-Kittle <jamesgk@google.com>
2 files changed