Fix savestates sometimes wiping thread stacks

Sequence of events during a load state:

1. Load memory.
2. Destruct threads, automatically zeroing out memory.
3. Create new threads and restore their state.
4. Crash because the thread's stack is all zeroed out now.

Could've been affecting many other games than FF1, and could've only randomly caused problems depending on the threads.  Ugh.

Verified all other destructors, they don't have this problem.

-[Unknown]