计算异常概率时会有除数为0的问题

[忘川]

pyod/pyod/models/base.py

Line 236 in 66010dd

 self._sigma * np.sqrt(2)) 

在这一行中，有可能会有标准差为0的情况，导致出现RuntimeWarning: divide by zero encountered in true_divide。
虽然这个不太影响程序运行，但还是希望做一下处理
感谢

[Yue Zhao]

if self._sigma == 0, which means all the scores are equal, then maybe the problem/ algorithm already fails...