plugin XEP-0277: better resilience to broken items:

- if `author` element can't be found, `publisher` attribute, then `IQ`'s `from` attributes
  are used as fallback to find author jid
- fix categories (tags) parsing if `author` element is not found
- remove items which have failed parsing from `mbGet` results (instead of using `None`).

sat/plugins/plugin_xep_0060.py

@@ -1181,7 +1181,10 @@ class XEP_0060(object):
             log.warning(f"Error while parsing item: {failure_.value}")
 
         d = defer.gatherResults([item_cb(item).addErrback(eb) for item in items])
-        d.addCallback(lambda parsed_items: (parsed_items, metadata))
+        d.addCallback(lambda parsed_items: (
+            [i for i in parsed_items if i is not None],
+            metadata
+        ))
         return d
 
     def serDList(self, results, failure_result=None):