NFS: check for req==NULL in nfs_try_to_update_request cleanup

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/write.c

@@ -682,6 +682,7 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
 		req->wb_bytes = rqend - req->wb_offset;
 out_unlock:
 	spin_unlock(&inode->i_lock);
+	if (req)
 		nfs_clear_request_commit(req);
 	return req;
 out_flushme: