Lookup neighbor chunks more efficiently in async lighting

Spigot-Server-Patches/Configurable-async-light-updates.patch

@@ -159,9 +159,9 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        final List<Chunk> neighbors = new ArrayList<Chunk>();
 +        for (int cx = (x >> 4) - 1; cx <= (x >> 4) + 1; ++cx) {
 +            for (int cz = (z >> 4) - 1; cz <= (z >> 4) + 1; ++cz) {
-+                if (this.chunkProvider.isChunkLoaded(cx, cz)) {
-+                    Chunk neighbor = this.getChunkAt(cx, cz);
-+                    if (neighbor != chunk) {
++                if (cx != x >> 4 && cz != z >> 4) {
++                    Chunk neighbor = this.getChunkIfLoaded(cx, cz);
++                    if (neighbor != null) {
 +                        neighbor.pendingLightUpdates.incrementAndGet();
 +                        neighbor.lightUpdateTime = chunk.world.getTime();
 +                        neighbors.add(neighbor);