block: misplaced rq_complete tracepoint

The rq_complete tracepoint was never issued for empty requests,
causing the resulting blktrace information to never show any
completion for those request.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-core.c

@@ -2400,11 +2400,11 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
 {
 	int total_bytes;
 
+	trace_block_rq_complete(req->q, req, nr_bytes);
+
 	if (!req->bio)
 		return false;
 
-	trace_block_rq_complete(req->q, req, nr_bytes);
-
 	/*
 	 * For fs requests, rq is just carrier of independent bio's
 	 * and each partial completion should be handled separately.