(issue1754) Handle inverted presentation in BedDifference exporter This als removes dead (would have triggered an exception in pdf export) code to handle beddiff results which are not "BedDiffYearResults"

SYMBOLSET
SYMBOL
  NAME 'point'
  TYPE ELLIPSE
  POINTS
    1 1
  END
  FILLED TRUE
END
SYMBOL
  NAME "square"
  TYPE VECTOR
  POINTS
    0 0
    0 1
    1 1
    1 0
    0 0
  END
  FILLED TRUE
END
END