Bug swiftshader:15

Change-Id: I27fe7bd2f0deaf19fab2f4565574ad084c49cddb
Reviewed-on: https://swiftshader-review.googlesource.com/7954Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-on: https://swiftshader-review.googlesource.com/8159Reviewed-by: Alexis Hétu <sugoi@google.com>