Fix another roster issue.

Caused by same issue of a JID being in the roster, but with an
incomplete entry.

sleekxmpp/basexmpp.py

@@ -640,7 +640,8 @@ class BaseXMPP(XMLStream):
             log.debug("%s %s got offline" % (jid, resource))
             del connections[resource]
 
-            if not connections and not self.roster[jid]['in_roster']:
+            if not connections and \
+               not self.roster[jid].get('in_roster', False):
                 del self.roster[jid]
             if not was_offline:
                 self.event("got_offline", presence)