Error in invokaton of struct.unpack in method unsubscribe?

[wnelis]

In file mqtt_as/__init__.py, line 560 in method unsubscribe reads:

    struct.pack_into("!BH", pkt, sz, pid)

I think it should be:

    struct.pack_into("!BH", pkt, 1, sz, pid)

[peterhinch]

Thanks for the report.

This does look like a bug. @bobveringa Do you agree that this fix is correct?

[bobveringa]

Looking at the docs and surrounding code this does seem like a correct fix.

Interesting that this hasn't caused issues before.

[peterhinch]

@bobveringa Indeed. Your views on #164 would also be appreciated. The original assumption behind mqtt_as (also the official library) was that topic names would be short.