core&ui: fix bugs (#672)

Co-authored-by: panda <panda_dtdyy@outlook.com>

packages/ui-default/templates/partials/problem_files.html

@@ -6,7 +6,8 @@
     <blockquote class="note">
       <p>{{ _('This is a copy of another problem.') }}</p>
     </blockquote>
-  {% elif _files.length %}
+  {% endif %}
+  {% if _files.length %}
     <table class="data-table {{ filetype }}-table">
       <colgroup>
         {% if not sidebar %}<col class="col--checkbox">{% endif %}
@@ -53,7 +54,7 @@
         {%- endfor -%}
       </tbody>
     </table>
-  {% else %}
+  {% elif not reference %}
     {{ nothing.render('No {0} at current.', compact=sidebar, args=[_(filetype)]) }}
   {% endif %}
-</div>
+</div>