Fix the wrong header test, found by Ferllings

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/branches/fork@1641 b32b6428-25c9-4566-ad07-03861ab6144f

lib/xaal/lib/messages.py

@@ -103,7 +103,7 @@ class MessageFactory(object):
             msg.targets = json.loads(data_rx['targets'])
             msg.version = data_rx['version']
             msg_time    = data_rx['timestamp'][0]
-        except KeyError:
+        except (KeyError, IndexError):
             raise MessageParserError("Bad Message, wrong fields")
 
         # Replay attack, window fixed to CIPHER_WINDOW in seconds