[stability-calculations] Rosetta issue

[j0kaso]

Rosettas keep-ligand script does not tolerate lines without a chain-id (e.g. TER lines). This needs to be added before (or this script changed)

• need to add note in the documentation/wiki

Rosetta/source/src/apps/public/relax_w_allatom_cst/clean_pdb_keep_ligand.py