ARTEMIS-4569 Improving order in which the list is added versus cancel…

… call

I just did some static analysis of this code, and I believe it would be better to first add to the list
before setting the cancel task.

Reason for that is in case the Runnable is dequeued between the add in the deQueue and setting the cancel task.

Possibility is remote but my OCD wouldn't let me ignore this small possibility.

artemis-server/src/main/java/org/apache/activemq/artemis/core/paging/impl/PagingStoreImpl.java

@@ -1035,8 +1035,8 @@ public boolean checkMemory(final Runnable runWhenAvailable, Consumer<AtomicRunna
    }
 
    private void addToBlockList(AtomicRunnable atomicRunnable, Consumer<AtomicRunnable> accepted) {
-      onMemoryFreedRunnables.add(atomicRunnable);
       atomicRunnable.setCancel(onMemoryFreedRunnables::remove);
+      onMemoryFreedRunnables.add(atomicRunnable);
       if (accepted != null) {
          accepted.accept(atomicRunnable);
       }