SPIGOT-7225: FireworkMeta#getPower() can throw a NullPointerException for items with no power set

By: Parker Hawke <hawkeboyz2@hotmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaFirework.java

@@ -389,7 +389,7 @@ class CraftMetaFirework extends CraftMetaItem implements FireworkMeta {
 
     @Override
     public int getPower() {
-        return this.power;
+        return hasPower() ? this.power : 0;
     }
 
     @Override