Fix issue that may be caused by trying to get a block in unloaded chunk

src/main/java/net/seanomik/energeticstorage/tasks/HopperTask.java

@@ -91,6 +91,7 @@ public class HopperTask extends BukkitRunnable {
     public void run() {
         for (Map.Entry<UUID, List<ESSystem>> systemEntry : Reference.ES_SYSTEMS.entrySet()) {
             for (ESSystem system : systemEntry.getValue()) {
+                if (system.getLocation().isWorldLoaded()) {
                     Block systemBlock = system.getLocation().getBlock();
 
                     // Get all relative hoppers touching the system.
@@ -124,6 +125,7 @@ public class HopperTask extends BukkitRunnable {
                 }
             }
         }
+    }
 
     @Override
     public synchronized void cancel() throws IllegalStateException {