lost: Fix to track more than one lost sector per owner

lost: Fix to track more than one lost sector per owner

makelost() overwrites an existing entry for the same thing, else
creates a new one.  It calls findlost() to find existing entries.
findlost() means to look up by coordinates if it's looking for a
sector entry, and by ID if it's looking for a ship, plane, land unit
or nuke entry.  It actually does both for sectors.  Since callers pass
zero ID for sectors, sector entries always match, so at most one gets
created, and additional ones overwrite it.

Broken since the lost table was introduced in 4.0.7.  Fix the flawed
comparison in findlost().

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