No need to clone here and it's not null checked

Fixes #1864

src/main/java/com/gmail/nossr50/skills/alchemy/AlchemyPotionBrewer.java

@@ -101,7 +101,7 @@ public final class AlchemyPotionBrewer {
         }
 
         for (int i = 0; i < 3; i++) {
-            ItemStack item = inventory.getItem(i).clone();
+            ItemStack item = inventory.getItem(i);
 
             if (isEmpty(item) || item.getType() == Material.GLASS_BOTTLE || !PotionConfig.getInstance().isValidPotion(item)) {
                 continue;