zlib: backport null dereference fix

zlib: backport null dereference fix

The curl developers found test case that crashed in their testing when
using zlib patched against CVE-2022-37434, same patch we've backported
in commit 7df6795d4c25 ("zlib: backport fix for heap-based buffer
over-read (CVE-2022-37434)"). So we need to backport following patch in
order to fix issue introduced in that previous CVE-2022-37434 fix.

References: https://github.com/curl/curl/issues/9271
Fixes: 7df6795d4c25 ("zlib: backport fix for heap-based buffer over-read (CVE-2022-37434)")
Signed-off-by: Petr Štetiar <ynezz@true.cz>