If the Buffer object's length is zero, or equal to the underlying
buffer object's length, `parent` property returns `undefined`.
> new Buffer(0).parent
undefined
> new Buffer(Buffer.poolSize).parent
undefined
This patch makes the buffer objects to consistently expose the buffer
object via the `parent` property, always.
Fixes: https://github.com/nodejs/node/issues/8266
PR-URL: https://github.com/nodejs/node/pull/8311
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
