load_nfl_rosters pre- and post-2002 columns not matching

[christophermclement]

Getting an error from:

sdv.nfl.load_nfl_rosters(list(range(1999, 2005)))

Leading to the error:

`ShapeError: unable to append to a dataframe of width 30 with a dataframe of width 36

The columns that don't exist in the earlier seasons are:

ngs_position week game_type status_description_abbr football_name draft_number