Simplify 1 pixel padding calculation

Change-Id: I780182ef9d39a19e1b9795b615733091d22f8f63
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265519
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed