Fix the wrong header test, found by Ferllings

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/branches/fork@1640 b32b6428-25c9-4566-ad07-03861ab6144f

lib/xaal/lib/messages.py

@@ -99,19 +99,15 @@ class MessageFactory(object):
 
         # Instanciate Message
         msg = Message()
-
-        if 'targets'in data_rx:
+        try:
             msg.targets = json.loads(data_rx['targets'])
-        elif 'version' in data_rx:
             msg.version = data_rx['version']
-        elif 'timestamp' in data_rx:
-            msg.timestamp = data_rx['timestamp']
-        else:
-            raise MessageFactoryParserError("Bad Message, wrong fields")
+            msg_time    = data_rx['timestamp'][0]
+        except KeyError:
+            raise MessageParserError("Bad Message, wrong fields")
 
         # Replay attack, window fixed to CIPHER_WINDOW in seconds
         now = build_timestamp()[0]  # test done only on seconds ...
-        msg_time = data_rx['timestamp'][0]
 
         if msg_time < (now - config.cipher_window):
             raise MessageParserError("Potential replay attack, message too old")