A panic was seen related to the buffer being reset in
one goroutine while being read in another. In the case
of pigz an early cancellation will cause the reader to
close, resetting the buffer and signaling the process
to shut down, but races since the process must stop
reading before the reset otherwise the a panic may occur.
This fix guarantees that the bufio is always reset and
returned to the pool on the same goroutine that is
doing the read. If a buffer is not fully read the
buffered reader should just be discarded and not
returned back to the pool.

Signed-off-by: Derek McGowan <[email protected]>