fix: can not get currentContext in error handler

[gxkl]

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.96 ⚠️

Comparison is base (34519d1) 99.61% compared to head (5747938) 98.66%.

❗ Current head 5747938 differs from pull request most recent head 933c837. Consider uploading reports for the commit 933c837 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             v2.x    #1757      +/-   ##
==========================================
- Coverage   99.61%   98.66%   -0.96%     
==========================================
  Files           5        5              
  Lines         521      523       +2     
  Branches      145      146       +1     
==========================================
- Hits          519      516       -3     
- Misses          2        7       +5     

Impacted Files	Coverage Δ
lib/application.js	94.77% <100.00%> (-3.71%)	⬇️

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[fengmk2]

• koa@2.14.2