Have BufferOutput respect buffer size

[thesmartwon]

I'm having trouble making a long lived BufferOutput since its constructor requires a pointer to a Buffer. It feels wrong to allocate Buffer on the heap for a stable pointer since it's just a std::vector that already allocates its storage on the heap.

An easy fix is this patch to BufferOutput:

BufferOutput::BufferOutput(Buffer* buf)
    : buf_(buf)
-    , pos_(0)
+    , pos_(buf->size())

Is there any reason not to do this?

[Enmk]

Hi @thesmartwon could you please elaborate on what you are trying to achieve? Also, if you see any obvious hickups or bugs in the code, please feel free to submit a PR