Bug swiftshader:15

Change-Id: I69184dcb70f4a4082a25420a0dade7bc87a8027e
Reviewed-on: https://swiftshader-review.googlesource.com/7957Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-on: https://swiftshader-review.googlesource.com/8162Reviewed-by: Alexis Hétu <sugoi@google.com>