python loader breaks sys.path[0]

- OpenCV => 4.x / 3.4.3+

```py
>>> import sys
>>> sys.path[0]
''
>>> import cv2
>>> sys.path[0]
'/usr/local/lib/python3.6/dist-packages/cv2/python-3.6'
```

https://docs.python.org/3.7/library/sys.html
> As initialized upon program startup, the first item of this list, path[0], is the directory containing the script that was used to invoke the Python interpreter.
