Initialize buffers on a pooled authenticated socket

When the buffers weren't initialized, it was causing a segfault when
there were events on the socket.

Change-Id: I74fede31ae10afdfec7c5286f2448b75191ab920
Reviewed-on: http://review.couchbase.org/34695
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Subhashni Balakrishnan <b.subhashni@gmail.com>