[CentOS] Fix for CVE-2020-1971 on CentOS 6.10

Simon Matter wrote:
>Since security updates for CentOS 6 are not provided anymore, I've decided
>to try my best to address CVE-2020-1971 and I welcome others to do the
>same for this and other new issues which may come up.

Thanks to Simon for doing this.

I made my own patch which ended up the same as Simon's apart from
whitespace and formatting.  It's been deployed on a CentOS 6 system that
can't be upgraded yet due to... reasons.  Seems to work in the limited
testing I've done.

Cheers,

Ron