Fix memory corruption bug in zlib

Fix memory corruption bug in zlib

zlib has a crashing bug. The bug fix has been sitting in the
unreleased develop branch for nearly four years. Pull in this fix.

ok mbuhl millert

Reported by Tavis Ormandy on oss-security:
https://marc.info/?l=oss-security&m=164809382107156&w=2

commit 5c44459c3b28a9bd3283aaceab7c615f8020c531
Author: Mark Adler <madler@alumni.caltech.edu>
Date:   Tue Apr 17 22:09:22 2018 -0700

    Fix a bug that can crash deflate on some input when using Z_FIXED.

    This bug was reported by Danilo Ramos of Eideticom, Inc. It has
    lain in wait 13 years before being found! The bug was introduced
    in zlib 1.2.2.2, with the addition of the Z_FIXED option. That
    option forces the use of fixed Huffman codes. For rare inputs with
    a large number of distant matches, the pending buffer into which
    the compressed data is written can overwrite the distance symbol
    table which it overlays. That results in corrupted output due to
    invalid distances, and can result in out-of-bound accesses,
    crashing the application.

    The fix here combines the distance buffer and literal/length
    buffers into a single symbol buffer. Now three bytes of pending
    buffer space are opened up for each literal or length/distance
    pair consumed, instead of the previous two bytes. This assures
    that the pending buffer cannot overwrite the symbol table, since
    the maximum fixed code compressed length/distance is 31 bits, and
    since there are four bytes of pending space for every three bytes
    of symbol space.

https://github.com/madler/zlib/commit/5c44459c3b28a9bd3283aaceab7c615f8020c531