publishing before advertising issue

[matteo-pacher]

While publishing at high rates, it could happen that the topic hasn't been properly advertised yet. Then the publishing happens before the actual advertisement. This creates an error on the Rosbridge WebSocket server like:
[ERROR] [1545148346.445662]: [Client 0] [id: publish:/robot_command:32] publish: integer out of range for 'I' format code

Implement a return in the advertise(self) function (src\roslibpy/core.py) and introduce a ready_event in the publish() function?