show an error dialog when a transport answers wrongly to register request. Fixes #1702

src/common/connection.py

@@ -1674,6 +1674,11 @@ class Connection:
 		if realm == common.xmpp.NS_REGISTER:
 			if event == common.xmpp.features_nb.REGISTER_DATA_RECEIVED:
 				# data is (agent, DataFrom, is_form)
+				if not data[1]: # wrong answer
+					self.dispatch('ERROR', (_('Invalid answer'),
+						_('Transport %s answered wrongly to register request.') % \
+						data[0]))
+					return
 				if self.new_account_info and\
 				self.new_account_info['hostname'] == data[0]:
 					#it's a new account

src/common/xmpp/features_nb.py

@@ -119,7 +119,11 @@ def _ReceivedRegInfo(con, resp, agent):
 	iq=Iq('get',NS_REGISTER,to=agent)
 	if not isResultNode(resp): 
 		return
-	df=resp.getTag('query',namespace=NS_REGISTER).getTag('x',namespace=NS_DATA)
+	tag=resp.getTag('query',namespace=NS_REGISTER)
+	if not tag:
+		con.Event(NS_REGISTER,REGISTER_DATA_RECEIVED,(agent,None,False))
+		return
+	df=tag.getTag('x',namespace=NS_DATA)
 	if df:
 		con.Event(NS_REGISTER,REGISTER_DATA_RECEIVED,(agent,DataForm(node=df),True))
 		return