Margherita custom slice ingredient holder fix

[CrabmansWorld]

See line 187-189

About The Pull Request

Fixes margherita slices so that they don't default to the generic pizza slice

Why it's Good for the Game

Removes the bugged state from custom slices

Proof of Testing

To test:

1. Spawn /obj/item/food/pizzaslice/margherita

2. View variables and click on the ingredient_holder datum to verify it's initialized properly

3. Spawn any /obj/item/food that the holder can contain and add it to the custom slice
4. The slice should retain its previous description and icon state, the only thing that has to change is the overlay

Changelog

🆑 Deadindamind
fix: custom margherita slices no longer default to an error icon
/:cl:

[XeonMations]

Proof of testing is supposed to be a visual of you testing the thing btw <3