Fix custom merchant trade event world reference

Author: kennytv

patches/server/0542-Add-PlayerTradeEvent-and-PlayerPurchaseEvent.patch

@@ -219,7 +219,7 @@ index d41f44ed2e497ba3373d170c08488b49e88334c4..d3a99ba6f3085ad12b67ddc94cc4ab39
 
      void notifyTradeUpdated(ItemStack stack);
 diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
-index 257776a12ca26c1e75be22a67c94b0aa012fd687..02fc14d84df08d9e0418691f6c6b71f013e16365 100644
+index 257776a12ca26c1e75be22a67c94b0aa012fd687..5074e8b2259b3fb969bd0ff99c296b7537920273 100644
 --- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
 +++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMerchantCustom.java
 @@ -74,10 +74,25 @@ public class CraftMerchantCustom extends CraftMerchant {
@@ -235,7 +235,7 @@ index 257776a12ca26c1e75be22a67c94b0aa012fd687..02fc14d84df08d9e0418691f6c6b71f0
 +                    merchantRecipe.increaseUses();
 +                }
 +                if (event == null || event.isRewardingExp()) {
-+                    this.tradingWorld.addFreshEntity(new net.minecraft.world.entity.ExperienceOrb(tradingWorld, tradingPlayer.getX(), tradingPlayer.getY(), tradingPlayer.getZ(), merchantRecipe.getXp(), org.bukkit.entity.ExperienceOrb.SpawnReason.VILLAGER_TRADE, this.tradingPlayer, null));
++                    this.tradingPlayer.level.addFreshEntity(new net.minecraft.world.entity.ExperienceOrb(tradingPlayer.level, tradingPlayer.getX(), tradingPlayer.getY(), tradingPlayer.getZ(), merchantRecipe.getXp(), org.bukkit.entity.ExperienceOrb.SpawnReason.VILLAGER_TRADE, this.tradingPlayer, null));
 +                }
 +            }
 +            this.notifyTrade(merchantRecipe);