set_data() can destroy communication

[hansu]

If you pass data ≠0 with id = 0 to set_data(), the DMX data stream will be incorrect, because the first data byte is expected as zero.

To prevent this, the user data could start at zero like this:

    def set_data(self,id,data):
        self.data[id+1]=data

or something like this:

    def set_data(self,id,data):
        if id == 0:
             return
        self.data[id]=data