be less restrictive when loading dictionaries

[mhekkel]

Density-fitness chocked on a file containing this:

loop_
_pdbx_database_related.db_name
_pdbx_database_related.details
_pdbx_database_related.db_id
_pdbx_database_related.content_type
PDB . XXXX re-refinement
. . . "associated SAS data"
. . . unspecified