Do not save pointer to 'struct passwd' returned by getpwnam etc.

Do not save pointer to 'struct passwd' returned by getpwnam etc.

- This pointer is to a static area which can change on further
  calls to getpwnam, getpwuid etc.
  Same with struct group returned by getgrnam.

  As the only field later referred to is uid or gid, fix
  by saving them instead.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230306053346.796992-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26332.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 62024046dffd6ff10309b791cd6600fe80bc46e3)