potentially fix logged out users getting an internal server error

app/templates/threads/thread.html

@@ -32,7 +32,7 @@
           <input class="warn" type="submit" value="{{"Unlock thread" if thread.is_locked else "Lock thread"}}">
         </form>
       {% endif %}
-      {% if active_user.is_mod() %}
+      {% if active_user and active_user.is_mod() %}
         <form class="modform" action="{{ url_for("threads.sticky", slug=thread.slug) }}" method="post">
           <input type=hidden name='target_op' value="{{ (not thread.is_stickied) | int }}">
           <input class="warn" type="submit" value="{{"Unsticky thread" if thread.is_stickied else "Sticky thread"}}">