Core: fix item links around core changes (ArchipelagoMW#2452)

BaseClasses.py

@@ -113,6 +113,11 @@ def extend(self, regions: Iterable[Region]):
             for region in regions:
                 self.region_cache[region.player][region.name] = region
 
+        def add_group(self, new_id: int):
+            self.region_cache[new_id] = {}
+            self.entrance_cache[new_id] = {}
+            self.location_cache[new_id] = {}
+
         def __iter__(self) -> Iterator[Region]:
             for regions in self.region_cache.values():
                 yield from regions.values()
@@ -220,6 +225,7 @@ def add_group(self, name: str, game: str, players: Set[int] = frozenset()) -> Tu
                 return group_id, group
         new_id: int = self.players + len(self.groups) + 1
 
+        self.regions.add_group(new_id)
         self.game[new_id] = game
         self.player_types[new_id] = NetUtils.SlotType.group
         world_type = AutoWorld.AutoWorldRegister.world_types[game]
@@ -617,7 +623,7 @@ class CollectionState():
     additional_copy_functions: List[Callable[[CollectionState, CollectionState], CollectionState]] = []
 
     def __init__(self, parent: MultiWorld):
-        self.prog_items = {player: Counter() for player in parent.player_ids}
+        self.prog_items = {player: Counter() for player in parent.get_all_ids()}
         self.multiworld = parent
         self.reachable_regions = {player: set() for player in parent.get_all_ids()}
         self.blocked_connections = {player: set() for player in parent.get_all_ids()}