title: Django Prefetching Nested FKs not working
body: <p>I have been working on this for a bit but I cannot seem to get prefetching to work correctly in my instance. I am trying to run a nested <code>Prefetch()</code> to prefetch items from a prefetched object, but the attribute is not being stored as usual. Can somebody please show me what I am doing wrong?</p>
  <p>Here is my code:</p>
  <pre><code>primary_residents = Resident.objects.filter(
          property=request.session['property'], type='primary', user__is_active=True
      ).select_related(
          'unit', 'unit__building', 'user'
      ).prefetch_related(
          Prefetch('current_balance',
                   queryset=Balance.objects.filter(is_active=True).prefetch_related(
                       Prefetch('charges',
                                queryset=Charges.objects.filter(date_entered__range=(
                                        previous_month, property.close_out_start_date_plus_one()), reversed=False
                                ).prefetch_related(
                                    'code', 'balance'),
                                to_attr='previous_charges'
                                )
                   ), to_attr='active_balance'
                   ),
      )
  for p in primary_residents:
      # errors out, previous_charges is not a valid attr
      print(p.active_balance.previous_charges)
  
  </code></pre>