whitespace at beginning of database accessions parsed from Stockholm files

Whilst fixing JAL-3529 - noticed that database refs imported from Stockhom's #GS AC tag have an additional space at the beginning.

Not sure if this has any real sideffect but the space prevents DBRef accession comparators from matching to dbrefs with non-whitespace containing accession fields for the same accession, which may result in duplicate database references being created.