fix issue with link to visit for generic appointments

smash/web/templates/appointments/edit.html

@@ -28,10 +28,12 @@
                 <a href="javascript:history.back(1)" class="btn btn-block btn-default">Go
                     back (discard changes)</a>
             </p>
-            <p class="col-md-2 pull-right">
-                <a href="{% url 'web.views.visit_details' appointment.visit.id %}" type="button"
-                   class="btn btn-block btn-default">View corresponding visit</a>
-            </p>
+            {% if appointment.visit %}
+                <p class="col-md-2 pull-right">
+                    <a href="{% url 'web.views.visit_details' appointment.visit.id %}" type="button"
+                       class="btn btn-block btn-default">View corresponding visit</a>
+                </p>
+            {% endif %}
         </div>
         <div class="box box-info">