fix: fix publications list crash with unspecified journal

scipost_django/affiliates/templates/affiliates/affiliatepublication_list.html

@@ -7,7 +7,9 @@
 {% block breadcrumb_items %}
   <span class="breadcrumb-item">Affiliates</span>
   <span class="breadcrumb-item"><a href="{% url 'affiliates:journals' %}">Journals</a></span>
-  <span class="breadcrumb-item"><a href="{% url 'affiliates:journal_detail' slug=journal.slug %}">{{ journal }}</a></span>
+  {% if journal %}  
+    <span class="breadcrumb-item"><a href="{% url 'affiliates:journal_detail' slug=journal.slug %}">{{ journal }}</a></span>
+  {% endif %}
   <span class="breadcrumb-item">Publications</span>
 {% endblock %}