Don't allow FAWE to "deadlock" itself when post-processing history by switching to the primary ForkJoinPool

- With enough chunks waiting to write to history, it's possible to fill the secondary fork pool up with locked threads, and thus prevent any threads from actually writing their history.

worldedit-core/src/main/java/com/boydti/fawe/object/changeset/AbstractChangeSet.java

@@ -351,7 +351,7 @@ public abstract class AbstractChangeSet implements ChangeSet, IBatchProcessor {
             wrappedTask.run();
             return Futures.immediateCancelledFuture();
         } else {
-            return Fawe.get().getQueueHandler().async(wrappedTask);
+            return Fawe.get().getQueueHandler().submit(wrappedTask);
         }
     }
 }