Bug swiftshader:15

Change-Id: I3f670be22415433a0582b3335fb48040e5a171c3
Reviewed-on: https://swiftshader-review.googlesource.com/7790Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-on: https://swiftshader-review.googlesource.com/8141Reviewed-by: Alexis Hétu <sugoi@google.com>