bugfix: parser incompletion was causing queue backlog...

In some now-common situation that wasn't being triggered before,
  the HTTP parser never completed even though we received
  a successful response, which in turn exposed a bug where
  the purger would not advance through the queue in those
  conditions, resulting in a fast loop re-sending the same
  PURGE over and over and over.... This seems to fix it.

Change-Id: Ib18a086e74e971aafeb809fe84adbfecf0b5eff9