pdb remarks: TLS group residue range can be null or missing
pdb remarks: TLS group residue range can be null or missing

fixes problem reported by Rob, with parsing:
3jum,3jvg,3ke6,3npe,5o0t,3piz,3pj2,6r7d,2x6p,4y8n,1ryq,1yrq

project-gemmi/gemmi,project-gemmi/gemmi,project-gemmi/gemmi,project-gemmi/gemmi