next/script creates unhandled promise rejection with empty error for every script that fails to load

[SkylarWolfLA]

What version of Next.js are you using?

11

What version of Node.js are you using?

12.14.1

What browser are you using?

Chrome

What operating system are you using?

macOS

How are you deploying your application?

next start

Describe the Bug

Loading any script which fails to load generates an unhandled rejection error "Uncaught (in promise) undefined"

This is due to this code

https://github.com/vercel/next.js/blob/canary/packages/next/client/script.tsx#L58

const loadPromise = new Promise<void>((resolve, reject) => {
    el.addEventListener('load', function () {
      resolve()
      if (onLoad) {
        onLoad.call(this)
      }
    })
    el.addEventListener('error', function () {
      reject()
      if (onError) {
        onError()
      }
    })
  })

reject is called but loadPromise never has an error handler attached unless you create two tags for the same script which will do ScriptCache.get(src).then(onLoad, onError)

Expected Behavior

No unhandled rejection error for errors and pass the real error to the onError

To Reproduce

<Script
        src="https://somebrokenlink.doesntexist"
        strategy="lazyOnload"
        onLoad={() => {
          console.log('success');
        }}
        onLoad={(e) => {
          console.log('error');
          console.log(e); // this doesn't exist either
        }}
      />

[balazsorban44]

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