Fix experience reward flag gets lost during MerchantRecipe conversion

By: blablubbabc <lukas@wirsindwir.de>

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

@@ -26,6 +26,7 @@ public class CraftMerchantRecipe extends MerchantRecipe {
                 maxUses,
                 this
         );
+        this.setExperienceReward(experienceReward);
     }
 
     @Override