Currently the check was incorrect as it did not consider the (unlikely) case of fd == 0. In order to fix this we should first correctly initialize it to -1, as the swrast implementations leave it set to zero (props to calloc()). Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com> Reviewed-by: Boyan Ding <boyan.j.ding@gmail.com>