Error: Assingning a previously freed instance when quitting to the main menu while there is a container in proximity

[snipercup]

Steps to reproduce:

• Go to a mob and kill it. It should drop loot
• Open the inventory and observe the loot container is visible in the inventory window
• Press escape and quit to main menu
• Observe error

The error originates from this line:

Dimensionfall/Scripts/item_manager.gd

Line 118 in 7343079

for inventory: InventoryStacked in proximityInventories.values():

Which is called from this line:

Dimensionfall/Scripts/item_manager.gd

Line 506 in 7343079

func _on_inventory_item_removed(item, inventory):

I'm not sure why that last line is called or what is removing items from the inventory. A quick fix would be to check if the game is started or is ending and not call update_accessible_items_list. We might need more diagnosis on the problem before we can come to a proper solution.

It might be because of this line:
https://github.com/Khaligufzel/Dimensionfall/pull/456/files#diff-26149249834a47c9270bbfda64bfd9dc5c7cda14578eace1de0fc26b8461a99aR355

But I'm not really sure.