core&ui: fix group filter display

packages/ui-default/templates/contest_main.html

@@ -60,14 +60,15 @@
         <div class="section__tools">
           <form method="get" name="filter-form">
             {{ _('Show') }}:
-          {% if groups.length %}
             <select class="inline compact select" name="group">
               <option value=""{% if not group %} selected{% endif %}>{{ _('All') }}</option>
               {%- for g in groups -%}
-                  <option value="{{ g }}"{% if group == g %} selected{% endif %}>{{ g }}</option>
+                <option value="{{ g }}"{% if group == g %} selected{% endif %}>{{ g }}</option>
               {%- endfor -%}
+              {%- if not groups|length -%}
+                <option disabled>{{ _('No group available') }}</option>
+              {%- endif -%}
             </select>
-          {% endif %}
             <select class="inline compact select" name="rule">
               <option value=""{% if not rule %} selected{% endif %}>{{ _('All') }}</option>
               {%- for k, v in model.contest.RULES -%}