Fixed crystals being able to be used on unintended items

eco-core/core-plugin/src/main/java/com/willfp/ecoarmor/upgrades/listeners/CrystalListener.java

@@ -49,6 +49,10 @@ public class CrystalListener extends PluginDependent implements Listener {
             return;
         }
 
+        if (ArmorUtils.getSetOnItem(current) == null) {
+            return;
+        }
+
         if (current.getType() == Material.AIR) {
             return;
         }