fix: 支付宝响应空签名时签名验证逻辑错误的问题

[lazychanger]

fix: #992 #975

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.40%. Comparing base (3683c69) to head (fc0681b).

:exclamation: Current head fc0681b differs from pull request most recent head 6456456

Please upload reports for the commit 6456456 to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #998 +/- ## ========================================= Coverage 97.40% 97.40% - Complexity 907 909 +2 ========================================= Files 347 347 Lines 6202 6206 +4 ========================================= + Hits 6041 6045 +4 Misses 161 161 ```

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[yansongda]

@lazychanger 我优化了下，麻烦帮忙看看有啥问题没？

[lazychanger]

没问题 @yansongda