Don't instantiate degenerate 2pt gradients

We can catch the condition at construction time, no need to defer.

Change-Id: I973b9e1b79998e2b334e3a91694c793882dfd65a
Reviewed-on: https://skia-review.googlesource.com/26564
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
3 files changed