Fix preferences view

- Use new objectgetter_optional
- Fix template

aleksis/core/templates/dynamic_preferences/sections.html

@@ -9,7 +9,7 @@
     {% for section in registry.section_objects.values %}
       <li class="tab">
         <a class="{% if active_section == section.name %}active{% endif %}"
-           href="{% url registry_url section %}"
+           href="{% url registry_url section.name %}"
            target="_self">
           {{ section.verbose_name }}
         </a>

aleksis/core/views.py

@@ -413,14 +413,14 @@ def preferences(request: HttpRequest, registry_name: str = "person", pk: Optiona
             raise PermissionDenied()
     elif registry_name == "person":
         registry = person_preferences_registry
-        instance = get_person_by_pk(request, pk)
+        instance = objectgetter_optional(Person, "request.user.person", True)(request, pk)
         form_class = PersonPreferenceForm
 
         if not request.user.has_perm("core.change_person_preferences", instance):
             raise PermissionDenied()
     elif registry_name == "group":
         registry = group_preferences_registry
-        instance = get_group_by_pk(request, pk)
+        instance = objectgetter_optional(Group)(request, pk)
         form_class = GroupPreferenceForm
 
         if not request.user.has_perm("core.change_group_preferences", instance):