Fix error when trying to close LayeredResourcePack where the filesystem is null.

Author: leMaik

chunky/src/java/se/llbit/chunky/resources/LayeredResourcePacks.java

@@ -109,6 +109,9 @@ public Path getRootPath() throws IOException {
 
     @Override
     public void close() throws IOException {
+      if (fileSystem == null) {
+        return;
+      }
       try {
         fileSystem.close();
       } catch (UnsupportedOperationException e) {