Fix issue with Reward Item changing (#84).

This issue may happened because Player#getInventory()#addItem(ItemStack) tries to add element into existing items in player inventory. If it did not manage to add it, it splits it in parts. This splitting created this issue.
It was fixed, by using clone of reward items, instead of using original elements.

pom.xml

@@ -6,7 +6,7 @@
 
 	<groupId>world.bentobox</groupId>
 	<artifactId>challenges</artifactId>
-	<version>0.5.0</version>
+	<version>0.5.1</version>
 
 	<name>Challenges</name>
 	<description>Challenges is an add-on for BentoBox, an expandable Minecraft Bukkit plugin for island-type games like SkyBlock, AcidIsland or CaveBlock.</description>

src/main/java/world/bentobox/challenges/panel/TryToComplete.java

@@ -210,7 +210,9 @@ public class TryToComplete
             // Item rewards
             for (ItemStack reward : this.challenge.getRewardItems())
             {
-                this.user.getInventory().addItem(reward).forEach((k, v) ->
+                // Clone is necessary because otherwise it will chane reward itemstack
+                // amount.
+                this.user.getInventory().addItem(reward.clone()).forEach((k, v) ->
                     this.user.getWorld().dropItem(this.user.getLocation(), v));
             }
 
@@ -247,7 +249,9 @@ public class TryToComplete
             // Item Repeat Rewards
             for (ItemStack reward : this.challenge.getRepeatItemReward())
             {
-                this.user.getInventory().addItem(reward).forEach((k, v) ->
+                // Clone is necessary because otherwise it will chane reward itemstack
+                // amount.
+                this.user.getInventory().addItem(reward.clone()).forEach((k, v) ->
                     this.user.getWorld().dropItem(this.user.getLocation(), v));
             }
 
@@ -280,7 +284,9 @@ public class TryToComplete
                     // Item rewards
                     for (ItemStack reward : level.getRewardItems())
                     {
-                        this.user.getInventory().addItem(reward).forEach((k, v) ->
+                        // Clone is necessary because otherwise it will chane reward itemstack
+                        // amount.
+                        this.user.getInventory().addItem(reward.clone()).forEach((k, v) ->
                             this.user.getWorld().dropItem(this.user.getLocation(), v));
                     }