Fix(frontend): ワードミュートがnullの時にもセンシティブミュートが行われるように

[tai-cha]

What

一部環境でセンシティブミュートが効かない可能性がある

Why

#15195 (comment)

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 18.83%. Comparing base (a3d236c) to head (c858f5d).
Report is 566 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #15364       +/-   ##
============================================
- Coverage    41.74%   18.83%   -22.92%     
============================================
  Files         1549      764      -785     
  Lines       196555   111027    -85528     
  Branches      2767     1233     -1534     
============================================
- Hits         82055    20907    -61148     
+ Misses      113939    89533    -24406     
- Partials       561      587       +26     

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[mi-gh-maintainer]

Thank you 🙏