Symfony version(s) affected: 4.3 Symfony Asset component

Description

Symfony Asset JsonManifestVersionStrategy doesn't work with UrlPackage.

How to reproduce

I'm creating a MediaWiki Skin and the CSS is generated from https://invent.kde.org/websites/aether-sass using Symfony Encore. The code is:

$urlPackage = new UrlPackage(
    'https://cdn.kde.org/',
    new JsonManifestVersionStrategy('https://cdn.kde.org/aether-devel/version/manifest.json')
);

$out->addStyle( $urlPackage->getUrl('aether-devel/version/bootstrap.css'), 'all' );

Possible Solution

I created a potential patch: https://invent.kde.org/websites/aether-mediawiki/blob/master/JsonManifestNetworkStrategy.php that remove the check that the file exist and instead check if file_get_contents($this->manifestPath) returned something. If this solution is good enough to be accepted, I will create a pull request :)

PS: I hope it's the right place to report a bug in Symfony component