kgo: avoid noise on consumer assignment

Author: twmb

Diff for: pkg/kgo/consumer_direct.go

@@ -65,7 +65,9 @@ func (cl *Client) AssignPartitions(opts ...DirectConsumeOpt) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	c.unassignPrior()
+	if c.typ != consumerTypeUnset {
+		c.unassignPrior()
+	}
 
 	d := &directConsumer{
 		topics:     make(map[string]Offset),

Diff for: pkg/kgo/consumer_group.go

@@ -265,7 +265,9 @@ func (cl *Client) AssignGroup(group string, opts ...GroupOpt) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	c.unassignPrior()
+	if c.typ != consumerTypeUnset {
+		c.unassignPrior()
+	}
 
 	ctx, cancel := context.WithCancel(cl.ctx)
 	g := &groupConsumer{