Add IItemDb#isReady to check if item database is available

Essentials/src/com/earth2me/essentials/api/IItemDb.java

@@ -153,4 +153,11 @@ public interface IItemDb {
     default Material getFromLegacy(final int id, final byte damage) {
         return MaterialUtil.convertFromLegacy(id, damage);
     }
+
+    /**
+     * Check whether the item database is loaded and ready for use.
+     *
+     * @return Whether items have finished loading
+     */
+    boolean isReady();
 }

Essentials/src/com/earth2me/essentials/items/AbstractItemDb.java

@@ -27,6 +27,8 @@ import static com.earth2me.essentials.I18n.tl;
 
 public abstract class AbstractItemDb implements IConf, net.ess3.api.IItemDb {
 
+    protected boolean ready = false;
+
     @Override
     public List<ItemStack> getMatching(User user, String[] args) throws Exception {
         List<ItemStack> is = new ArrayList<>();
@@ -224,4 +226,9 @@ public abstract class AbstractItemDb implements IConf, net.ess3.api.IItemDb {
 
         return sb.toString().trim().replaceAll("§", "&");
     }
+
+    @Override
+    public boolean isReady() {
+        return ready;
+    }
 }

Essentials/src/com/earth2me/essentials/items/FlatItemDb.java

@@ -59,9 +59,12 @@ public class FlatItemDb extends AbstractItemDb {
             .collect(Collectors.joining());
 
         this.loadJSON(String.join("\n", json));
+
+        ready = true;
     }
 
     private void reset() {
+        ready = false;
         items.clear();
         itemAliases.clear();
         allAliases.clear();

Essentials/src/com/earth2me/essentials/items/LegacyItemDb.java

@@ -44,6 +44,7 @@ public class LegacyItemDb extends AbstractItemDb {
             return;
         }
 
+        ready = false;
         durabilities.clear();
         items.clear();
         names.clear();
@@ -115,6 +116,8 @@ public class LegacyItemDb extends AbstractItemDb {
         }
 
         LOGGER.info(String.format("Loaded %s items from items.csv.", listNames().size()));
+
+        ready = true;
     }
 
     @Override