assault attack board lboard paradrop: Fix defending land unit supply

assault attack board lboard paradrop: Fix defending land unit supply

get_dlist() collects defending land units in a list, and resupplies
them.  Bug: it uses a local copy instead of the one in the list.  When
att_fight() writes back the list, the commodities supplied get wiped
out, triggering a seqno oops.  Broken in commit 62b9399cd "subs:
Factor lnd_insque() out of lnd_sel(), ask_olist(), ...", v4.3.33.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>