Fixes NULL dereference in SSL_check_chain() for TLS 1.3, marked with
high severity, assigned CVE-2020-1967.
Ref: https://www.openssl.org/news/secadv/20200421.txt
Cherry-pick from openwrt/openwrt@3773ae1.
Also add mirror for mainland China user in this commit.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: CN_SZTL <cnsztl@project-openwrt.eu.org>
Co-authored-by: Petr Štetiar <ynezz@true.cz>