fix: can not get currentContext in error handler

[gxkl]

pick from 1757

Checklist

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

[codecov[bot]]

Codecov Report

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

Comparison is base (bec13ec) 99.61% compared to head (c931e72) 98.66%.

:exclamation: Current head c931e72 differs from pull request most recent head 2c6482c. Consider uploading reports for the commit 2c6482c to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1758 +/- ## ========================================== - 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](https://codecov.io/gh/koajs/koa/pull/1758?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=koajs) | Coverage Δ | | |---|---|---| | [lib/application.js](https://codecov.io/gh/koajs/koa/pull/1758?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=koajs#diff-bGliL2FwcGxpY2F0aW9uLmpz) | `94.61% <100.00%> (-3.83%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=koajs). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=koajs)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[fengmk2]

npm dist-tag ls
experimental: 3.0.0-alpha.1 latest-0: 0.21.1 latest: 2.14.2 next: 2.14.2 v1: 1.7.0