Add fallback for world_gen_settings.dat

Paper servers modify the world structure a little which stopped Amulet from opening the world.
With this small modification, Paper worlds can be opened as well as worlds where that file does not exist for some reason.

Author: gentlegiantJGC

amulet/level/formats/anvil_world/format.py

@@ -246,11 +246,35 @@ def _register_dimension(
     def _get_dimenion_bounds(self, dimension_type_str: Dimension) -> SelectionGroup:
         if self.version >= 2709:  # This number might be smaller
             if self.version >= 4786:  # This number might be smaller
-                world_gen_settings = load_nbt(
-                    os.path.join(
-                        self.path, "data", "minecraft", "world_gen_settings.dat"
+                world_gen_settings_path = os.path.join(
+                    self.path, "data", "minecraft", "world_gen_settings.dat"
+                )
+                if not os.path.isfile(world_gen_settings_path):
+                    world_gen_settings_path = os.path.join(
+                        self.path,
+                        "dimensions",
+                        "minecraft",
+                        "overworld",
+                        "data",
+                        "minecraft",
+                        "world_gen_settings.dat",
+                    )
+                if os.path.isfile(world_gen_settings_path):
+                    world_gen_settings = load_nbt(
+                        world_gen_settings_path
+                    ).compound.get_compound("data", CompoundTag())
+                else:
+                    world_gen_settings = CompoundTag(
+                        {
+                            "dimensions": CompoundTag(
+                                {
+                                    dimension_type_str: CompoundTag(
+                                        {"type": StringTag("minecraft:overworld")}
+                                    )
+                                }
+                            )
+                        }
                     )
-                ).compound.get_compound("data", CompoundTag())
             else:
                 # If in a version that supports custom height data packs
                 world_gen_settings = self.root_tag.compound.get_compound(