clone itemstack to return remaining stack (#6353)

patches/server/Make-hoppers-respect-inventory-max-stack-size.patch

@@ -21,6 +21,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
                  stack = ItemStack.EMPTY;
 +                // Paper start
 +                } else {
++                    stack = stack.copy(); // Paper - copy stack to return leftover stack
 +                    stack.setCount(originalCount - stack.getCount());
 +                }
 +                // Paper end