Hide usernames for anonymous posts.

lms/templates/discussion/_underscore_templates.html

@@ -26,7 +26,9 @@
           <h1>${'<%- title %>'}</h1>
           <p class="posted-details">
               <span class="timeago" title="${'<%- created_at %>'}">${'<%- created_at %>'}</span> by
+              ${"<% if (!obj.anonymous) { %>"}
               <a href="${'<%- user_url %>'}">${'<%- username %>'}</a>
+              ${"<% } else {print('anonymous');} %>"}
               <span class="post-status-closed top-post-status" style="display: none">
                 &bull; This thread is closed.
               </span>