Fix NPE in SkylightManager

src/main/java/com/falsepattern/chunk/internal/vanilla/SkylightManager.java

@@ -57,6 +57,20 @@ public class SkylightManager extends NibbleManager implements DataManager.SubChu
         }
     }
 
+    @Override
+    public void writeToBuffer(Chunk chunk, ExtendedBlockStorage blockStorage, ByteBuffer buffer) {
+        if (!chunk.worldObj.provider.hasNoSky) {
+            super.writeToBuffer(chunk, blockStorage, buffer);
+        }
+    }
+
+    @Override
+    public void readFromBuffer(Chunk chunk, ExtendedBlockStorage blockStorage, ByteBuffer buffer) {
+        if (!chunk.worldObj.provider.hasNoSky) {
+            super.readFromBuffer(chunk, blockStorage, buffer);
+        }
+    }
+
     @Override
     public boolean subChunkPrivilegedAccess() {
         return true;