(svn r2807) Fix two major bugs in the threaded save code:

- Do not dereference a local variable which no longer exists; this lead to random crashes when saving
- (Win32) Do not close a handle before it is used last
There are still many major problems (race conditions and resulting memory corruption/crashes) left

os2.c

@@ -647,12 +647,6 @@ bool CreateOTTDThread(void *func, void *param)
 	return(true);
 }
 
-void CloseOTTDThread(void)
-{
-	_endthread();
-	return;
-}
-
 void JoinOTTDThread(void)
 {
 	if (thread1 == 0)