pkg/kgo direct consumer: do not consume topics with no partitions

If a topic has a load error, findNewAssignments will return new
assignments for topics that have no partitions. This emits extraneous
log lines and looks like progress is being made when it isn't,

pkg/kgo/consumer_direct.go

@@ -99,7 +99,7 @@ func (d *directConsumer) findNewAssignments() map[string]map[int32]Offset {
 		// the topic is explicitly specified.
 		if useTopic {
 			partitions := topicPartitions.load()
-			if d.cfg.regex && partitions.isInternal {
+			if d.cfg.regex && partitions.isInternal || len(partitions.partitions) == 0 {
 				continue
 			}
 			toUseTopic := make(map[int32]Offset, len(partitions.partitions))