fix(vue-app): handle promise rejection from asyncData

[rchl]

When exception is thrown during handling of asyncData, Nuxt catches it and shows server error but it also chains returned promise without using catch. This results in unhandled promise rejection.

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

The original code

nuxt/packages/vue-app/template/server.js

Lines 320 to 325 in e5efc25

	const promise = promisify(Component.options.asyncData, app.context)
	promise.then((asyncDataResult) => {
	ssrContext.asyncData[Component.cid] = asyncDataResult
	applyAsyncData(Component)
	return asyncDataResult
	})

gets the asyncData promise and chains it to applyAsyncData. That then doesn't run when asyncData has thrown but since this promise is not further chained (especially to catch) it effectively makes it an unhandled promise rejection error.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codesandbox]

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[codecov-commenter]

Codecov Report

Base: 66.18% // Head: 66.18% // No change to project coverage 👍

Coverage data is based on head (b970d5f) compared to base (2c6b593).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##              2.x   #18585   +/-   ##
=======================================
  Coverage   66.18%   66.18%           
=======================================
  Files          93       93           
  Lines        4096     4096           
  Branches     1158     1158           
=======================================
  Hits         2711     2711           
  Misses       1119     1119           
  Partials      266      266           

Flag	Coverage Δ
unittests	66.18% <ø> (ø)

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[rchl]

any prospects for getting this merged?