Using zmemzero to initialize deflate_state

Due to its history, zlib has to support building for environments
without access to basic C functions (e.g. memcpy, memset, etc) or in
environments with odd memory management patterns (e.g. MSDOS).

Therefore, it is good form to use zmemset/zmemcpy/etc for handling
memory and the same applies for initializing a memory block to zero.

Bug: 1032721
Change-Id: I8d898872ca00197cc7e961d7c49e1912073895c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2016772


Reviewed-by: Chris Blume <cblume@chromium.org>
Reviewed-by: vikas soni <vikassoni@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#734686}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bcdbc75cd3f832ad0527a00f5bf56aa437abf1f6