Fix passing queryset to as_sepadd

Closes #13

aleksis/apps/tezor/forms.py

@@ -25,7 +25,7 @@ send_emails_action.permission = "tezor.send_invoice_email"
 def get_sepa_xml(modeladmin, request, queryset):
     """Get a SEPA XML for selected invoices."""
     qs = SEPAMandate.objects.filter(payment__in=queryset, payment__status=PaymentStatus.PREAUTH)
-    sepadd = SEPAMandate.as_sepadd(qs)
+    sepadd = SEPAMandate.as_sepadd(qs=qs)
 
     return HttpResponse(
         sepadd.export(pretty_print=True).decode(),