Fix overflow in blur for VERY wide bitmaps.

UBSAN has identified an int overflow in a byte offset calculation.

BUG=skia:7698

Change-Id: Ia9687c15bb63dc2953de5d9b9aad764a24e73a57
Reviewed-on: https://skia-review.googlesource.com/113710
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed