Fixes #237 (Empty ByteBuf leak)

The code was not sending an `onNext` call for empty buffers.
This resulted in leaking memory for empty payload responses as the release of `ByteBuf` was a part of the `onNext` call.

 This change sends the content `onNext` unconditionally and lets the user decide what to do with the buffer.
Merge pull request #242 from NiteshKant/0.x

Fixes #237 (Empty ByteBuf leak)