Fix certain layouts leaking empty slots into next data

worlds/sc2/mission_order/structs.py

@@ -217,8 +217,7 @@ def fill_depths(self) -> None:
             # Check for accessible missions
             cur_missions: Set[SC2MOGenMission] = {
                 mission for mission in next_missions
-                if not mission.option_empty
-                and mission.is_unlocked(beaten_missions)
+                if mission.is_unlocked(beaten_missions)
             }
             if len(cur_missions) == 0:
                 raise Exception(f"Mission order ran out of accessible missions during iteration {iterations}")
@@ -231,9 +230,7 @@ def fill_depths(self) -> None:
                 # If the beaten missions at depth X unlock a mission, said mission can be beaten at depth X+1 
                 mission.min_depth = mission.entry_rule.get_depth(beaten_missions) + 1
                 new_next = [
-                    next_mission for next_mission in mission.next
-                    if not next_mission.option_empty
-                    and not (
+                    next_mission for next_mission in mission.next if not (
                         next_mission in cur_missions
                         or next_mission in beaten_missions
                         or next_mission in new_beaten_missions
@@ -710,23 +707,15 @@ def __init__(self, world: World, parent: ReferenceType[SC2MOGenCampaign], name:
                 mission.next = [self.missions[idx] for idx in mission.option_next]
 
         # Set up missions' prev data
-        seen_missions: Set[SC2MOGenMission] = set()
-        cur_missions: List[SC2MOGenMission] = [mission for mission in self.entrances]
-        while len(cur_missions) > 0:
-            mission = cur_missions.pop()
-            seen_missions.add(mission)
+        for mission in self.missions:
             for next_mission in mission.next:
                 next_mission.prev.append(mission)
-                if next_mission not in seen_missions and \
-                   next_mission not in cur_missions:
-                    cur_missions.append(next_mission)
 
         # Remove empty missions from access data
         for mission in self.missions:
             if mission.option_empty:
                 for next_mission in mission.next:
-                    if mission in next_mission.prev:
-                        next_mission.prev.remove(mission)
+                    next_mission.prev.remove(mission)
                 mission.next.clear()
                 for prev_mission in mission.prev:
                     prev_mission.next.remove(mission)