Make proc summary robust against empty template_latex_tgz

proceedings/templates/partials/proceedings/summary.html

@@ -41,6 +41,10 @@
   </tr>
   <tr>
     <th>Templates</th>
-    <td><a href="{{ proceedings.template_latex_tgz.url }}">LaTeX (gzipped tarball)</a></td>
+    <td>
+      {% if proceedings.template_latex_url %}
+	<a href="{{ proceedings.template_latex_tgz.url }}">LaTeX (gzipped tarball)</a>
+      {% endif %}
+    </td>
   </tr>
 </table>