[fix] 修复JSONPath.set()空指针问题

[mimajiushi]

What this PR does / why we need it?

• 修复此问题: [BUG] JSONPath.set()空指针异常 #2145

[CLAassistant]

All committers have signed the CLA.

[wenshao]

请签署CLA

[mimajiushi]

请签署CLA

没看懂怎么签，我看早期PR没有，或者你修了把这个PR关掉吧

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (67e1e74) 75.37% compared to head (c1b371e) 75.36%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
...in/java/com/alibaba/fastjson2/JSONPathSegment.java	16.66%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2146      +/-   ##
============================================
- Coverage     75.37%   75.36%   -0.01%     
- Complexity    21637    21642       +5     
============================================
  Files           634      634              
  Lines         85368    85383      +15     
  Branches      18920    18928       +8     
============================================
+ Hits          64343    64351       +8     
- Misses        13109    13111       +2     
- Partials       7916     7921       +5     

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[wenshao]

已经合入，欢迎以后继续参与进来！