Prevent "ValueError: need more than 1 value to unpack" errors when getting incomplete data from TVRage

I was getting errors like this:

```
INFO     SHOWQUEUE-FORCE-UPDATE :: Checking the last aired episode to see if the dates match between TVDB and TVRage
DEBUG    SHOWQUEUE-FORCE-UPDATE :: Loading TVRage info from URL: http://services.tvrage.com/tools/quickinfo.php?show=XXXX
DB       CP Server Thread-4 :: cache.db: SELECT show_name FROM scene_exceptions WHERE tvdb_id = ? with args [XXXX]
WARNING  SHOWQUEUE-FORCE-UPDATE :: Error encountered while checking TVRage<->TVDB sync: need more than 1 value to unpack
DEBUG    SHOWQUEUE-FORCE-UPDATE :: Traceback (most recent call last):
  File "/xxx/sickbeard/tvrage.py", line 123, in confirmShow
    info = self._getTVRageInfo(curSeason, 1)
  File "/xxx/sickbeard/tvrage.py", line 262, in _getTVRageInfo
    key, value = x.split("@")
ValueError: need more than 1 value to unpack
```

This error stops the processing, and no covers/posters would be downloaded.

The patch in this merge request checks if we are able to split using "@" before actually splitting, thus resulting in successful cover/poster downloads. :smiley: