Bug swiftshader:20

Change-Id: I20c2ab7cb4c00c365520ff8b8500f7594127498b
Reviewed-on: https://swiftshader-review.googlesource.com/8468Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>