consumer group bugfix: map needs to be one block lower

topicOffsets is meant to track per-topic offsets when updating
uncommitted. Thus, we want to have the maps existence be per-topic.

The prior location had the map per fetch, and would reuse that map
across all topics within a fetch.

pkg/kgo/consumer_group.go

@@ -1433,13 +1433,13 @@ func (g *groupConsumer) updateUncommitted(fetches Fetches) {
 	defer g.mu.Unlock()
 
 	for _, fetch := range fetches {
-		var topicOffsets map[int32]uncommit
 		for _, topic := range fetch.Topics {
 
 			if g.cl.cfg.logger.Level() >= LogLevelDebug {
 				fmt.Fprintf(&b, "%s[", topic.Topic)
 			}
 
+			var topicOffsets map[int32]uncommit
 			for _, partition := range topic.Partitions {
 				if len(partition.Records) == 0 {
 					continue