ui: fix problem_files

packages/ui-default/templates/problem_files.html

@@ -11,7 +11,7 @@
             <a href="{{ url('problem_config', pid=pdoc.docId) }}" class="primary rounded button">{{ _('Config') }}</a>
             <button class="primary rounded button" name="create_testdata">{{ _('Create') }}</button>
             <button class="primary rounded button" name="upload_testdata">{{ _('Upload') }}</button>
-          {% else %}
+          {% elif reference %}
             <a href="{{ url('problem_detail', domainId=pdoc.reference.domainId, pid=pdoc.reference.pid) }}" class="primary rounded button">{{ _('Source') }}</a>
           {% endif %}
         </div>