fs.read into zero buffer should not throw exception

[feross]

Given a file descriptor fd that references a non-zero-length file, I expect this code to work:

var buf = new Buffer(0)
// Read zero bytes into offset 0 of `buf`
fs.read(fd, buf, 0, 0, 0, function(err, bytesRead, buffer) {
  console.log('got buffer', buffer)
}

Instead it throws an exception because it assumes that offset is out bounds because it starts at the end of the buffer (based on the buffer's length). If length was a positive number, this would be out of bounds. But when length is 0, an offset that starts at the end of the buffer is fine.

I expect a buffer of length zero to be returned in the callback, with no error, and no thrown exception.

[feross]

Sent a PR that fixes the issue: #4518