Bug swiftshader:15

Change-Id: I6975f7a61ee232630b82e7844b8bc65088564827
Reviewed-on: https://swiftshader-review.googlesource.com/7959Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-on: https://swiftshader-review.googlesource.com/8164Reviewed-by: Alexis Hétu <sugoi@google.com>