rdkafka/producer: minor changes to poll()
rdkafka/producer: minor changes to poll()

Checking for ReferenceError is just noise since we always join() the
poller thread before stopping/finalising.

Signed-off-by: Yung-Chin Oei <e4c1ab9da74060df152545062ee274845648ed6c@yungchin.nl>

wikimedia/operations-debs-python-pykafka,wikimedia/operations-debs-python-pykafka,thedrow/samsa,thedrow/samsa,benauthor/pykafka,thedrow/samsa,benauthor/pykafka,benauthor/pykafka,wikimedia/operations-debs-python-pykafka