Do not allow recursive creation of multiblocks. (#4472)

src/main/java/appeng/me/cluster/IAECluster.java

@@ -28,5 +28,11 @@ public interface IAECluster {
 
     void destroy();
 
+    /**
+     * @return True if the cluster has been destroyed, but not yet removed from a
+     *         tile entity. Usually true during destruction.
+     */
+    boolean isDestroyed();
+
     Iterator<IGridHost> getTiles();
 }