Method try_add

ImGuiFileDialog.h:290–297

    }

    bool try_add(T vKey) {
        if (!exist(vKey)) {
            m_Dico[vKey] = m_Array.size();
            m_Array.push_back(vKey);
            return true;
        }
        return false;
    }

    bool try_set_existing(T vKey) {
        if (exist(vKey)) {