Bug swiftshader:20

Change-Id: I81ad267d450713ffe2a5a84e1d7f7f140b515c85
Reviewed-on: https://swiftshader-review.googlesource.com/8454Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>