GridFSBucketReadStream `doRead` does not honor chunk size

gridfs-stream\download.js
When using the GridFSBucket.openDownloadStream to read the data of the specified segment,for example, there is a file size of 2547447 bytes in the gridfs,the chunksize is 1024*1024,I use openDownloadStream(fileid,

) want get 1024 bytes,but return 364544 bytes.I find the error came from function doRead,I fix it then it's ok.