Fix for $base->level >= $start

I suppose you want all menu starting at some level, so use as `$base_id` the common parent before this level (or its root).
Example: I want all menu starting at 4, but `$active->level === 6`, therefore the common parent for level 4 menus will be at index (`6 - 4 - 1 =`) 1 in `$active->tree`.

`(!$showAll && $item->level > 1 && !in_array($item->parent_id, $path))`
In my opinion, this check is redundant. If you want to show all items, simply don't set `$end`, therefore the `$base_id` will be recognized as an ancestor of the deeper menus and they wouldn't be purged.