Fix memory leak after sighup

Fix memory leak after sighup

The c.es env_set is (re)allocated for each "sighup loop iteration", while
it was free'd only once at process shutdown.  Move the env_set_destroy()
call to match the same level as the env_set_create() call to fix that.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1535550583-21825-1-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17429.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 7170bef507bfe74ceb4a12f8f10df4d2d6ad39c9)