fix Wing Loading calculation in paraglider mode

if polar have Wing Area, when you edit basic setting, wing load is reseted to 5kg/m²

Bug Sample :
    MassDryGross : 120Kg
    Ballast : 0L
    WingArea : 32m²

max weigth is 120kg, but if you edit basic setting, weight calculated is 160kg

Fix :
change range and step of wing load parameter for allow wing load less than 5kg/m²