let read_res add structure even in non-resonance case

The method read_res sets structure[mat_id]['data'] for the first time, which is expected by other methods. If the LRP flag for the material is -1, there's no resonance data, and the method did not change anything.
So the small change added some lines to fill structure[mat_id]['data']  with a single entry for mat_id and empty values, even in case there is no resonance data to read.
Some PEP8 issues here, mostly it looks like you just need to add spaces after the colons (`:`)