Fix Shields in Multiworld

[MattEqualsCoder]

There's an issue with the multiworld code where if you pick up a shield for someone else, then get sent your own shield, you receive a free shield. To work around this, I made it so that shields are locked to your own world. For a starting point of where to look, according to someone in the main SMZ3 Discord:

cassidymoen — 12/14/2022 1:18 PM Without looking too deeply at it, my thinking is there's progressive shield flags in the highest two bits of $7EF416 (for alttpr, not sure how it's mapped in smz3 but offset $416 from the start of the save) The multiworld item is probably setting those flags while (correctly) not giving the item