Fix missing null check on terrainToTileNether

src/main/java/folk/sisby/antique_atlas/TerrainTiling.java

@@ -141,6 +141,7 @@ public static Pair<TerrainTileProvider, TileElevation> terrainToTileNether(World
         WorldTerrainSummary terrain = WorldSummary.of(world).terrain();
         if (terrain == null) return null;
         ChunkSummary chunk = terrain.get(pos);
+        if (chunk == null) return null; // Skip events fired for chunks we don't have yet (e.g. new shares)
         @Nullable LayerSummary.Raw lowSummary = chunk.toSingleLayer(null, NETHER_SCAN_HEIGHT, world.getTopY());
         @Nullable LayerSummary.Raw fullSummary = chunk.toSingleLayer(null, world.getBottomY() + world.getDimension().logicalHeight() - 1, world.getTopY());
         IndexedIterable<Biome> biomePalette = terrain.getBiomePalette(pos);