CoreStopWordDictionary.dictionary.clear()空指针

[zerofancy]

Describe the bug
A clear and concise description of what the bug is.

调用CoreStopWordDictionary.reload()后调用CoreStopWordDictionary.dictionary.clear()会空指针。

Code to reproduce the issue
Provide a reproducible test case that is the bare minimum necessary to generate the problem.

CoreStopWordDictionary.reload()
CoreStopWordDictionary.dictionary.clear()

Describe the current behavior
A clear and concise description of what happened.

执行CoreStopWordDictionary.dictionary.clear()时equivalenceClassMDAGNodeHashMap空指针异常。

Expected behavior
A clear and concise description of what you expected to happen.

正确清空停用词。

System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04):macOS Big Sur 11.0.1 20B29 x86_64.
• Python version:非python版本
• HanLP version:1.7.8

Other info / logs
Include any logs or source code that would be helpful to diagnose the problem. If including tracebacks, please include the full traceback. Large logs and files should be attached.

分析原因为StopWordDictionary.reload()时执行了MDAG.simplify()，其中有equivalenceClassMDAGNodeHashMap = null;

MDAGSet.clear()方法中equivalenceClassMDAGNodeHashMap.clear();没有判空。

相关：a57645c

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[hankcs]

感谢反馈，已经修复，请参考上面的commit。
如果还有问题，欢迎重开issue。