use SkIRect makeOffset to avoid overflows

Bug: oss-fuzz:7657
Change-Id: I7917306cf0a158d2e1f36611e85ef26028da9954
Reviewed-on: https://skia-review.googlesource.com/110280
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed