[Bleeding] DoubleChestInventory.getHolder() no longer returns null. Addresses BUKKIT-995

By: Celtic Minstrel <celtic.minstrel.ca@some.place>

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

@@ -1,5 +1,6 @@
 package org.bukkit.craftbukkit.inventory;
 
+import org.bukkit.block.DoubleChest;
 import org.bukkit.inventory.DoubleChestInventory;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.ItemStack;
@@ -50,4 +51,9 @@ public class CraftInventoryDoubleChest extends CraftInventory implements DoubleC
             right.setContents(rightItems);
         }
     }
+
+    @Override
+    public DoubleChest getHolder() {
+        return new DoubleChest(this);
+    }
 }