Fix double array increment in s_client mysql connect

The packet parsing code for the server version string was incrementing
the array index twice on every iteration. This meant that strings with
an even number of characters would pass, but strings with an odd number
(ex: 5.7.18-0ubuntu0.16.04.1) would cause the pos variable to get out
of sync.

This would cause a later failure with "MySQL packet is broken."

CLA: trivial

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3799)