Read big file issue with overflow

[se-m]

Node v 4.3.1
This code don`t work

if (overflow !== null) {
  buffer = overflow + buffer;
}

It actually decrease buffer length
This is my 2 chunks read log

read 65536
read + overflow 65536
record 93
overflow 86
read 65536
read + overflow 64298

The first record in 2nd chunk was parsed wrong.

---

Buffer.concat do the trick

if (overflow !== null) {
 buffer = Buffer.concat([overflow, buffer]);
}

3 chunk log
read 65536
read + overflow 65536
record 93
overflow 86
read 65536
read + overflow 65622
record 93
overflow 57
read 65536
read + overflow 65593