Fix bit shift overflow making bots sad

TBR=robertphillips@google.com
Change-Id: I8dee1a3c804bd7966e79da9d60ba1659f57525ee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407822
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
1 file changed