Fix Proper instance has no attribute 'size'

When findpropper call pickBestResult the instance as not attribute
'size'. Added a check.

sickbeard/search.py

@@ -242,6 +242,7 @@ def pickBestResult(results, show, quality_list=None):
                        logger.INFO)
             continue
 
+        if hasattr(cur_result, 'size'):
             if sickbeard.USE_FAILED_DOWNLOADS and failed_history.hasFailed(cur_result.name, cur_result.size,
                                                                            cur_result.provider.name):
                 logger.log(cur_result.name + u" has previously failed, rejecting it")