tools (sat_defer), plugin XEP-0060: added a function "stanza2NotFound" to convert item-not-found StanzaError to exceptions.NotFound in an errback

sat/plugins/plugin_xep_0060.py

@@ -611,6 +611,7 @@ class XEP_0060(object):
             )
             # we have no MAM data here, so we add None
             d.addCallback(lambda data: data + (None,))
+            d.addErrback(sat_defer.stanza2NotFound)
             d.addTimeout(TIMEOUT, reactor)
         else:
             # if mam is requested, we have to do a totally different query