NCBC-617: End operation when EndRead returns zero in SslConnection.

Change-Id: Id90d02312636f410d0b78c9fec80705c0fdc42b7
Reviewed-on: http://review.couchbase.org/41124
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>