Bug swiftshader:15

Change-Id: I6cfb3218a9962ca9fe271e9595ecf56aaca6375d
Reviewed-on: https://swiftshader-review.googlesource.com/7398Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>