Only show "post a comment" link if comments already exist

The purpose of the link is to help you jump past comments to the
comment box, and so...

Even with this new conditional, I'm not entirely sure I like that link ;)

mediagoblin/templates/mediagoblin/user_pages/media.html

@@ -62,7 +62,7 @@
         {%- endtrans %}
       </p>
       <h3></h3>
-      {% if request.user %}
+      {% if request.user and comments.count() %}
         <p><a href="#comment_form">{% trans %}Post a comment{% endtrans %}</a></p>
       {% endif %}
       {% if comments %}