Correctly handle empty outer blurs.

Most blur styles approach the original mask as the sigma goes to zero.
The outer style however approaches nothing as the mask sigma goes to
zero. Handle this case correctly.

Change-Id: I14f76e144d7cfc78aeaff30ff5444a21f1e5f98b
Reviewed-on: https://skia-review.googlesource.com/128006
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed