[BUKKIT-3451] Use correct item amount for FurnaceExtractEvent.

Also don't call FurnaceExtractEvent when the item amount is 0.

nms-patches/SlotFurnaceResult.patch

@@ -11,7 +11,7 @@
  public class SlotFurnaceResult extends Slot {
  
      private EntityHuman a;
-@@ -50,6 +55,17 @@
+@@ -50,6 +55,18 @@
                  i = j;
              }
  
@@ -20,10 +20,11 @@
 +            TileEntityFurnace furnace = ((TileEntityFurnace) this.inventory);
 +            org.bukkit.block.Block block = a.world.getWorld().getBlockAt(furnace.position.getX(), furnace.position.getY(), furnace.position.getZ());
 +
-+            FurnaceExtractEvent event = new FurnaceExtractEvent(player, block, org.bukkit.craftbukkit.util.CraftMagicNumbers.getMaterial(itemstack.getItem()), itemstack.count, i);
-+            a.world.getServer().getPluginManager().callEvent(event);
-+
-+            i = event.getExpToDrop();
++            if (b != 0) {
++                FurnaceExtractEvent event = new FurnaceExtractEvent(player, block, org.bukkit.craftbukkit.util.CraftMagicNumbers.getMaterial(itemstack.getItem()), b, i);
++                a.world.getServer().getPluginManager().callEvent(event);
++                i = event.getExpToDrop();
++            }
 +            // CraftBukkit end
 +
              while (i > 0) {