Fix shop visibility after respawn or world change

src/main/java/de/epiceric/shopchest/listeners/ShopUpdateListener.java

@@ -9,7 +9,10 @@ import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerChangedWorldEvent;
 import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.player.PlayerRespawnEvent;
+import org.bukkit.scheduler.BukkitRunnable;
 
 public class ShopUpdateListener implements Listener {
 
@@ -28,14 +31,43 @@ public class ShopUpdateListener implements Listener {
 
     @EventHandler(priority = EventPriority.MONITOR)
     public void onPlayerJoin(PlayerJoinEvent e) {
+        restartShopUpdater(e.getPlayer());
+    }
+
+    // The Bukkit::getOnlinePlayers() list does not include players that
+    // are currently respawning or chaning worlds, so when only one player is
+    // online and is currently respawning, the updater will think that no player
+    // is online, so it will stop. To prevent that, a delay of 1 tick is needed.
+
+    @EventHandler
+    public void onPlayerChangedWorld(final PlayerChangedWorldEvent e) {
+        new BukkitRunnable() {
+            @Override
+            public void run() {
+                restartShopUpdater(e.getPlayer());
+            }
+        }.runTaskLater(plugin, 1L);
+    }
+
+    @EventHandler
+    public void onPlayerRespawn(final PlayerRespawnEvent e) {
+        new BukkitRunnable() {
+            @Override
+            public void run() {
+                restartShopUpdater(e.getPlayer());
+            }
+        }.runTaskLater(plugin, 1L);
+    }
+
+    private void restartShopUpdater(Player p) {
         if (!plugin.getUpdater().isRunning()) {
             plugin.setUpdater(new ShopUpdater(plugin));
             plugin.getUpdater().start();
         }
 
         for (Shop shop : plugin.getShopUtils().getShops()) {
-            if (shop.getHologram() != null) shop.getHologram().hidePlayer(e.getPlayer());
+            if (shop.getHologram() != null) shop.getHologram().hidePlayer(p);
-            if (shop.getItem() != null) shop.getItem().setVisible(e.getPlayer(), false);
+            if (shop.getItem() != null) shop.getItem().setVisible(p, false);
         }
     }