Simplify --compress parsing in options.c

Simplify --compress parsing in options.c

This removes a level of identation and make the "stub" condition
easier to see.

Change-Id: Iae47b191f522625f81eedd3a237b272cb7374d90
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230323170601.1256132-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26501.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit bfc00a01c10bbdd9683aab5db2c2e7dcbb2f7378)