null_blk: Fix REQ_OP_ZONE_CLOSE handling

In order to match ZBC defined behavior, closing an empty zone must
result in the "empty" zone condition instead of the "closed" condition.

Fixes: da644b2c ("null_blk: add zone open, close, and finish support")
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_zoned.c

@@ -186,6 +186,9 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
 		if (zone->cond == BLK_ZONE_COND_FULL)
 			return BLK_STS_IOERR;
 
+		if (zone->wp == zone->start)
+			zone->cond = BLK_ZONE_COND_EMPTY;
+		else
 			zone->cond = BLK_ZONE_COND_CLOSED;
 		break;
 	case REQ_OP_ZONE_FINISH: