Add saveguard not to include 0 in a scale for logarithmic axes Including 0 or allowing negative values triggers a bug in the jfreechart logarithmic axis code that causes values < 1 to be drawn in carthesic coordinates. Fixes: flys/issue12345

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