off by one errors sure are nice

the item gets added to the vec before len is calculated, and since its
0-indexed we want to subtract 1

src/ship/items/inventory.rs

@@ -494,7 +494,7 @@ impl CharacterInventory {
             
             self.items.push(new_stacked_item);
             if let Some(InventoryItem::Stacked(new_item)) = self.items.last() {
-                Some((new_item, InventorySlot(self.count())))
+                Some((new_item, InventorySlot(self.count()-1)))
             }
             else {
                 None