Fix calling init_cleanup on shutdown

- Fixes saving audio volume
- Fix memeory leak warnings

Thanks to @de4me for pointing this out

Source/appfat.cpp

@@ -20,8 +20,6 @@ void __cdecl app_fatal(const char *pszFmt, ...)
 
 	va_end(va);
 
-	dx_cleanup();
-	init_cleanup();
 	exit(1);
 }
 

Source/diablo.cpp

@@ -254,11 +254,13 @@ void diablo_init(LPSTR lpCmdLine)
 
 	SFileEnableDirectAccess(TRUE);
 	init_archives();
+	atexit(init_cleanup);
 
 	UiInitialize();
 #ifdef SPAWN
 	UiSetSpawned(TRUE);
 #endif
+	atexit(UiDestroy);
 
 	ReadOnlyTest();
 
@@ -269,7 +271,9 @@ void diablo_init(LPSTR lpCmdLine)
 	diablo_parse_flags(lpCmdLine);
 
 	snd_init(NULL);
+	atexit(sound_cleanup);
 	sound_init();
+	atexit(effects_cleanup_sfx);
 }
 
 void diablo_splash()
@@ -294,7 +298,6 @@ int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLi
 	diablo_init(lpCmdLine);
 	diablo_splash();
 	mainmenu_loop();
-	UiDestroy();
 
 	return 0;
 }

Source/init.cpp

@@ -39,11 +39,7 @@ void init_cleanup()
 		hellfire_mpq = NULL;
 	}
 
-	UiDestroy();
-	effects_cleanup_sfx();
-	sound_cleanup();
 	NetClose();
-	dx_cleanup();
 }
 
 void init_create_window()
@@ -51,6 +47,7 @@ void init_create_window()
 	if (!SpawnWindow(PROJECT_NAME, SCREEN_WIDTH, SCREEN_HEIGHT))
 		app_fatal("Unable to create main window");
 	dx_init(NULL);
+	atexit(dx_cleanup);
 	gbActive = true;
 	gpBufStart = &gpBuffer[BUFFER_WIDTH * SCREEN_Y];
 	gpBufEnd = &gpBuffer[BUFFER_WIDTH * (SCREEN_HEIGHT + SCREEN_Y)];