Resetting consumer offsets to latest causes lag to show as -2

[yolken-segment]

If you run reset-offsets with --offset=-1, i.e. to reset the consumer group to the latest offset, the offsets show up as -2 in the lag output, e.g.:

Benjamins-MacBook-Pro:topicctl benjamin.yolken$ topicctl get lags --zk-addr=localhost:2181 topic-default test-consumer
[2020-08-25 16:02:20]  INFO Group member lags:
------------+--------------------------------+---------------+-------------+---------------+---------------------------+------------+-----------
  PARTITION |           MEMBER ID            | MEMBER OFFSET | MEMBER TIME | LATEST OFFSET |        LATEST TIME        | OFFSET LAG | TIME LAG  
------------+--------------------------------+---------------+-------------+---------------+---------------------------+------------+-----------
  0         | [email protected] | -2            |             | 5293          | 2020-08-25T16:02:20-07:00 | 5295       |           
  1         | [email protected] | -2            |             | 5293          | 2020-08-25T16:02:20-07:00 | 5295       |           
  2         | [email protected] | -2            |             | 5292          | 2020-08-25T16:02:20-07:00 | 5294       |           
------------+--------------------------------+---------------+-------------+---------------+---------------------------+------------+-----------

They're not actually -2 (i.e., earliest offset) in Kafka; this is just an artifact of this logic in kafka-go: https://github.com/segmentio/kafka-go/blob/bd93f32228e23a60cc087dea40d5f81a41ed34d0/client.go#L113. We should probably remove that logic from the previous function.