api: Fix bug in OrgDetail for non-existent Org

The OrgDetail view wasn't properly handling object-not-found errors.

datastore/api/org/api.py

@@ -72,14 +72,15 @@ def get_object(self):
             db.Publisher.objects.filter(getter_run__in=db.GetterRun.objects.in_use())
         )
 
-        organisation = models.Organisation.get(
-            org_id,
-            funder_queryset=funder_queryset,
-            recipient_queryset=recipient_queryset,
-            publisher_queryset=publisher_queryset,
-        )
-
-        if not organisation:
+        try:
+            organisation = models.Organisation.get(
+                org_id,
+                funder_queryset=funder_queryset,
+                recipient_queryset=recipient_queryset,
+                publisher_queryset=publisher_queryset,
+            )
+
+        except models.Organisation.DoesNotExist:
             raise Http404
 
         return organisation