Guard variable that's not always defined. (#418)

* guard variable that's not always defined

* adjust

Author: merwok

admin_interface/templates/admin/base_site.html

@@ -146,11 +146,13 @@
 {% if theme.list_filter_highlight %} list-filter-highlight {% endif %}
 {% if theme.list_filter_sticky %} list-filter-sticky {% endif %}
 
+{% if adminform and inline_admin_formsets %}
 {% admin_interface_use_changeform_tabs adminform inline_admin_formsets as admin_interface_use_changeform_tabs %}
 {% if admin_interface_use_changeform_tabs %}
     {% if theme.show_fieldsets_as_tabs %} show-fieldsets-as-tabs {% endif %}
     {% if theme.show_inlines_as_tabs %} show-inlines-as-tabs {% endif %}
 {% endif %}
+{% endif %}
 
 {% if theme.collapsible_stacked_inlines %} collapsible-stacked-inlines
     {% if theme.collapsible_stacked_inlines_collapsed %} collapsible-stacked-inlines-collapsed {% endif %}