Fix bug in db queue manager: when receiving an invalid or deleted notice, we were running it through the 'temporary fail, release it to try again' path instead of the 'done, discard item' path. Should fix some infinite-loop-of-doom-in-queue cases.

lib/dbqueuemanager.php

@@ -100,7 +100,7 @@ class DBQueueManager extends QueueManager
             }
         } else {
             $this->_log(LOG_INFO, "[$queue] Got empty/deleted item, discarding");
-            $this->_fail($qi);
+            $this->_done($qi);
         }
         return true;
     }