Mistake in Urcheon/Pak.py when processing list of built files

I spotted this in `Urcheon/Pak.py`:

```python
			head = unit["head"]
			body = unit["body"]
[…]
			# if multiple calls produce the same files (like merge_bsp)
			if head in unit:
				continue
```

That can't work, this is probably a leftover or we may have to do `if head in body` instead.
