Fixed a bucket of lava disappearing when used in a furnace (#3973)

fixes #2385

src/pocketmine/item/Bucket.php

@@ -50,6 +50,14 @@ class Bucket extends Item implements MaybeConsumable{
 		return 0;
 	}
 
+	public function getFuelResidue() : Item{
+		if($this->meta === Block::LAVA or $this->meta === Block::FLOWING_LAVA){
+			return ItemFactory::get(Item::BUCKET);
+		}
+
+		return parent::getFuelResidue();
+	}
+
 	public function onActivate(Player $player, Block $blockReplace, Block $blockClicked, int $face, Vector3 $clickVector) : bool{
 		$resultBlock = BlockFactory::get($this->meta);
 

src/pocketmine/item/Item.php

@@ -655,6 +655,16 @@ class Item implements ItemIds, \JsonSerializable{
 		return 0;
 	}
 
+	/**
+	 * Returns an item after burning fuel
+	 */
+	public function getFuelResidue() : Item{
+		$item = clone $this;
+		$item->pop();
+
+		return $item;
+	}
+
 	/**
 	 * Returns how many points of damage this item will deal to an entity when used as a weapon.
 	 */

src/pocketmine/tile/Furnace.php

@@ -152,8 +152,7 @@ class Furnace extends Spawnable implements InventoryHolder, Container, Nameable{
 		}
 
 		if($this->burnTime > 0 and $ev->isBurning()){
-			$fuel->pop();
+			$this->inventory->setFuel($fuel->getFuelResidue());
-			$this->inventory->setFuel($fuel);
 		}
 	}