cherenkov parameters fail for Tables (and some other types)

The kp.physics.cherenkov() fails for Table and a few other types due to a typo. It's an easy fix but I'd like to keep this open until we have tests so that there is also coverage. @zaly maybe you have time, otherwise I'll take care later...

Traceback (most recent call last):
  File "test.py", line 30, in <module>
    pipe.drain(5)
  File "/Users/tamasgal/Dev/km3pipe/venv/lib/python3.8/site-packages/thepipe/core.py", line 451, in drain
    results = self._drain(cycles)
  File "/Users/tamasgal/Dev/km3pipe/venv/lib/python3.8/site-packages/thepipe/core.py", line 383, in _drain
    new_blob = module(blob_to_send)
  File "/Users/tamasgal/Dev/km3pipe/venv/lib/python3.8/site-packages/thepipe/core.py", line 187, in __call__
    return self.process(*args, **kwargs)
  File "test.py", line 20, in process
    cherenkov_params = kp.physics.cherenkov(chits, bt)
  File "/Users/tamasgal/Dev/km3pipe/km3pipe/physics.py", line 106, in cherenkov
    out = _cherenkov(calib_pos, calib_dir, track_pos, track_dir, track_t)
UnboundLocalError: local variable 'track_pos' referenced before assignment