Ensures that under no circumstances storage-related harddels can brick HUDs (#93559)

## About The Pull Request

If something harddels with its reference still in ``open_containers``
due to whatever reasons, it will permanently brick HUDs of anyone who
had that storage open until their mob or HUD is reset by admins,
rendering the game completely unplayable. I'm not sure what exactly went
wrong as ``COMSIG_ATOM_EXITED`` should handle deletions already, but
[this runtime
log](https://terry-logs.tgstation13.org/2025/10/20/round-257110/runtime.log)
contains some info if anyone is willing to poke at the issue more.

I know this technically "silences the real problem" but the issue is
harddels caused by storage not being informed of item deletion, its
logged as a harddel and shouldn't brick clients while at it.

## Changelog
🆑
fix: Fixed an issue which could randomly completely break a player's
visuals until an admin resets their HUD
/🆑

code/_onclick/hud/hud.dm

@@ -345,6 +345,7 @@ GLOBAL_LIST_INIT(available_ui_styles, list(
 			if(always_visible_inventory.len)
 				screenmob.client.screen += always_visible_inventory
 			if(open_containers.len && screenmob == mymob) // Don't show open inventories to ghosts
+				list_clear_nulls(open_containers)
 				screenmob.client.screen += open_containers
 			screenmob.client.screen += toggle_palette