Fix: fix callback missing when metadata request failed

[aiquestion]

We experience this issue when main thread cgrp start to do a rebalance
and failed when parsing metadata, the cgrp callback will be lost
and result in consumer unassigned.

If rd_kafka_handle_Metadata failed and will not retry, need to enque
the callback with err.

[edenhill]

Good find!

[edenhill]

Thank you!