Fixed TT2 Skill Downgrading

/// <summary>
/// Determines if the first skill is parented by the second
/// </summary>
/// <param name="child"></param>
/// <param name="potentialParent"></param>
/// <returns></returns>
public bool IsSkillDescended(Skill child, Skill potentialParent)
{
    //require skills to belong here
    if (child == null || potentialParent == null || !Talents.Contains(child) || !Talents.Contains(potentialParent)) return false;
    if (child == potentialParent) return false;

    Skill s = child;
    while (s.prerequisite != null && s.prerequisite != potentialParent) s = s.prerequisite;
    return s.prerequisite == potentialParent;
}

/// <summary>
/// Attempts to lower the level of a skill.
/// Will fail if the skill cannot be lowered validly.
/// </summary>
/// <param name="skill"></param>
/// <returns></returns>
public bool CanDowngradeSkill(Skill skill)
{
    if (skill.CurLevel <= 0) return false;

    foreach (Skill s in Skills.Where((Skill x) => x.CurLevel > 0))
    {
        //can't close off a skill with live children
        if (IsSkillDescended(s, skill) && skill.CurLevel == 1) return false;

        //calculate the cost of every non-descendant at a lower req
        int specCost = 0;
        foreach (Skill k in Skills.Where((Skill x) => !IsSkillDescended(x, s) && x.spRequirement < s.spRequirement))
        {
            specCost += k.totalCost[k.CurLevel];
        }
        if (specCost < s.spRequirement) return false;
    }

    //it's a valid downgrade
    return true;
}