fix: handle plain HttpResponse from elevation SVG endpoint, unracked devices

- RackElevationOfflineSVGView called .render() unconditionally on the
  RackViewSet elevation action's response, but that action returns a
  plain HttpResponse (not a DRF Response) when render=svg is
  requested, causing AttributeError on every click.
- effective_width_positions() crashed with decimal.InvalidOperation
  when a device had no rack position set (e.g. surfaced via NetBox
  Topology Views, which includes unracked devices). Such devices now
  get the default full-width result instead of entering the Decimal
  conversion.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

netbox_utilities/views.py

@@ -391,7 +391,8 @@ class RackElevationOfflineSVGView(LoginRequiredMixin, View):
         api_request.user = request.user
         drf_view = RackViewSet.as_view({"get": "elevation"})
         response = drf_view(api_request, pk=rack.pk)
-        response.render()
+        if hasattr(response, "render"):
+            response.render()
 
         offline_svg = strip_svg_hyperlinks(response.content)
         filename = f"{rack.name}-{face}-offline.svg".replace(" ", "_")