Offsetted (relatively to sources) patches apply to wrong lines

`patch -p 1 < patchFile.patch` (GNU patch) works fine.

```python
def applyPatch(fileText: str, patchFile: Path):
	with patchFile.open("rb") as psf:
		ps = patch.PatchSet(psf)
		ps.parse(psf)

	p = ps.items[0]


	with BytesIO(fileText.encode("utf-8")) as sF:
		return b"".join(ps.patch_stream(sF, p.hunks)).decode("utf-8")
```

produces the wrong results.
