Don't crash if unparseable values exist on the failure queue.

We saw some jobs become unloadable on our resque queue, due to issues turning strangely-encoded strings into JSON and back. This meant that resque couldn't parse the jobs, and so we were seeing `nil` elements in the `failures` array.

This is the simplest way of preventing these malformed entries from preventing monitoring of the failures queue entirely.

lib/resque/server/views/failed.erb

@@ -16,6 +16,10 @@
     <% index += 1 %>
     <li>
       <dl>
+        <% if job.nil? %>
+        <dt>Error</dt>
+        <dd>Job <%= index%> could not be parsed; perhaps it contains invalid JSON?</dd>
+        <% else %>
         <dt>Worker</dt>
         <dd>
           <a href="<%= url(:workers, job['worker']) %>"><%= job['worker'].split(':')[0...2].join(':') %></a> on <b class='queue-tag'><%= job['queue'] %></b > at <b><span class="time"><%= job['failed_at'] %></span></b>
@@ -47,6 +51,7 @@
             <%=h job['error'] %>
           <% end %>
         </dd>
+        <% end %>
       </dl>
       <div class='r'>
       </div>