Handle fragmented atrac IDs better.

This avoids conflicts when ids are deleted.

Indeed fixes Lord of Arcana (at least the demo version.)  Didn't start at non-0 because it wasn't before, and from one test I suspect the PSP may start at 0... need to create more tests though.

Anyway, this is a minimal change that fixes things.

Pointed out by @oioitff.

-[Unknown]