Pass request to call to get_iterable in preview endpoint

This fixes the case where request-based query processors can cause
inconsistent results because get_queryset gets the request kwarg earlier
in the preview endpoint.

Signed-off-by: Don Naegely <naegelyd@gmail.com>
2.3.11 Final

Signed-off-by: Don Naegely <naegelyd@gmail.com>