Make sure soup has categories before parsing them

Fixes https://github.com/SickRage/sickrage-issues/issues/216

sickbeard/providers/newznab.py

@@ -119,7 +119,7 @@ class NewznabProvider(NZBProvider):
             return False, return_categories, error_string
 
         data = BeautifulSoup(data, 'html5lib')
-        if not self._checkAuthFromData(data):
+        if not self._checkAuthFromData(data) and data.caps and data.caps.categories:
             data.decompose()
             error_string = u"Error parsing xml for [%s]" % (self.name)
             logger.log(error_string, logger.DEBUG)