fix: Do not throw if appstore is unavailable during upgrade

[juliusknorr]

Instead of throwing an error we just return an empty list as it is also done if there was a previous error a few lines above and instead just log it.

Otherwise this may leave apps disabled that used to be enabled before:

server/lib/private/Updater.php

Lines 386 to 393 in dae7c15

	if (!empty($previousEnableStates)) {
	$ocApp = new \OC_App();
	if (!empty($previousEnableStates[$app]) && is_array($previousEnableStates[$app])) {
	$ocApp->enable($app, $previousEnableStates[$app]);
	} else {
	$ocApp->enable($app);
	}
	}

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

/backport to stable30