nfsd: fix corrupted reply to badly ordered compound

We're encoding a single op in the reply but leaving the number of ops
zero, so the reply makes no sense.

Somewhat academic as this isn't a case any real client will hit, though
in theory perhaps that could change in a future protocol extension.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -1735,6 +1735,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 	if (status) {
 		op = &args->ops[0];
 		op->status = status;
+		resp->opcnt = 1;
 		goto encode_op;
 	}