Fix for getting base id, when callback is defined

[DosMaster]

Fixes issue #107

[bemble]

Also waiting for this PR to be accepted :) For now, I did this:

tmp_communicator = SerialCommunicator(port=serial_path)
tmp_communicator.start()
base_id = tmp_communicator.base_id
if tmp_communicator.is_alive():
    tmp_communicator.stop()
communicator = SerialCommunicator(port=serial_path, callback=receive_callback)
communicator.base_id = base_id