iservice: return correct size when domains are truncated

iservice: return correct size when domains are truncated

In case not all domains can be converted in the available buffer, return
the size of the already converted domains size plus the second terminating
zero for the MULTI_SZ.

Reported-by: Marc Heuse <marc@srlabs.de>
Reported-by: stephan@srlabs.de
Change-Id: Iabad046c930dd0f38ec50d1c43d8b3288816df7d
Signed-off-by: Heiko Hund <heiko@ist.eigentlich.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1391
Message-Id: <20251126104315.4776-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg34680.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>