records: fix get_blob to ease transition.

• With the new uploader there is a new column inside bibfmt to allow different kind of versions of the record: master, DIP, etc. but bibupload is not filling this column, only format='xm' to identify the master version for marcxml.

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>