fix: check the asset's existence before running filter

[sodatea]

Fixes vuejs/vue-cli#4572

Apparently, the getAsset() call is possible to return an undefined value.

webpack/lib/Compilation.js

Lines 2058 to 2060 in 9c6b367

	getAsset(name) {
	if (!Object.prototype.hasOwnProperty.call(this.assets, name))
	return undefined;

What kind of change does this PR introduce?

A bugfix

Did you add tests for your changes?

Not sure how to get a minimum reproduction of this case but it's an emergency fix.

Does this PR introduce a breaking change?

No.

What needs to be documented once your changes are merged?

Nothing.

[webpack-bot]

For maintainers only:

• This need to be documented (issue in webpack/webpack.js.org will be filed when merged)

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[sokra]

Thanks

[trueleader]

This is not the only one, a few lines later the next break:

webpack/lib/performance/SizeLimitsPlugin.js

Lines 69 to 72 in e4c7d8c

	const fileFilter = name => {
	const asset = compilation.getAsset(name);
	return assetFilter(asset.name, asset.source, asset.info);
	};

[Akryum]

#9701