Made MtProtoSender multi-thread safe

This will allow you to, for example, send requests
when you get an update (if someone tells you something,
you can automatically reply something else). Beware,
this may lead to an infinite loop so add conditions!

main.py

@@ -74,8 +74,8 @@ if __name__ == '__main__':
                     date = datetime.fromtimestamp(msg.date)
                     print('[{}:{}] {}: {}'.format(date.hour, date.minute, name, msg.message))
 
-            # Send chat message
-            else:
+            # Send chat message (if any)
+            elif msg:
                 client.send_message(input_peer, msg, markdown=True, no_web_page=True)
 
     print('Thanks for trying the interactive example! Exiting...')