[5.x] Private asset container url method should return null

[jasonvarga]

This was always the intention, but it didn't.

Doing $asset->url() on a private asset would already return null, it's just calling on the container itself that had the issue.

This was discovered by doing Asset::findByUrl($url) and having a private S3 container.

cms/src/Assets/AssetRepository.php

Lines 75 to 83 in a9f4e41

	protected function resolveContainerFromUrl($url)
	{
	return AssetContainer::all()->sortByDesc(function ($container) {
	return strlen($container->url());
	})->first(function ($container, $id) use ($url) {
	return Str::startsWith($url, $container->url())
	|| Str::startsWith(URL::makeAbsolute($url), $container->url());
	});
	}

It would loop through all containers, get their urls, and figure out a matching container. When you had a private s3 container, getting its URL here would throw an exception. Now since it returns null the exception is avoided. The private container is skipped in findByUrl as expected, since they don't have URLs.