cn2num逻辑有些问题

[Chen1399]

cn2num()函数的compute_value()中last_power的设计有些问题，导致只能实现一次当前单位大于之前单位，比如试验 一亿零二百三十二万零五百三十五 .
应该改为：

        """
        Compute the value.
        When current unit is larger than previous unit, current unit * all previous units will be used as all previous units.
        e.g. '两千万' = 2000 * 10000 not 2000 + 10000
        """
        value = [0]
        last_power = 0
        for s in integer_symbols:
            if isinstance(s, CND):
                value[-1] = s.value
            elif isinstance(s, CNU):
                value[-1] *= pow(10, s.power)
                print(value)
                if s.power > last_power:
                    for i in range(len(value)-2,-1,-1):
                        if value[i]<pow(10, s.power):
                            value[i]*=pow(10, s.power)
                        else:
                            break
                last_power = s.power
                value.append(0)
        return sum(value)