Add missing validation for negative GLsizei values.

Change-Id: Id3022059b3d5c21e5c78c668e21fddf569d920ef
Reviewed-on: https://swiftshader-review.googlesource.com/3760
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>