correct postProcessor.py

Correct postProcessor.py, there was an error after "added xem for
incoherent tvdbvs scene release name" commit. We got None as tvdb_id
causing a lot of those errors :   File
"/usr/local/sickbeard/sickbeard/postProcessor.py", line 701, in
_get_ep_obj
self._log(("This show (tvdb_id=%d) isn't in your list, you need to add
it to SB before post-processing an episode" % tvdb_id), logger.ERROR)
TypeError: %d format: a number is required, not NoneType