Update 12.0.4 -> 12.0.5 brakes "share_folder" config.php option

[magentaco]

Steps to reproduce

1. Have existing Nextcloud 12.0.4 (and previous versions) running using "share_foler" in config.php
2. Use the webupdater to update to v12.0.5
3. Recognize that all user's "share_foler" is not accessible.
   The message "This directory is unavailable, please check the logs or contact the administrator" is shown on the webclient. PC-clients don't sync that directory any more.

Expected behaviour

The directory named by "shared_folder" should show all files that have been with myself.

Actual behaviour

Directory is inaccessible by browser and does not sync by PC-clients, iOS-client shows "request failed: internal server error (500)"
I did not recognize any related information in the logs (standard log level).

Server configuration

Operating system:
Debian 9

Web server:
apache

Database:
mariaDB

PHP version:
7.0

Nextcloud version: (see Nextcloud admin page)
see above

Updated from an older Nextcloud/ownCloud or fresh install:
Update via browser

[juliusknorr]

Please provide a more detailed bug report with a complete issue template filled out, especially logs are interesting, as stated in the message you've posted:

The message "This directory is unavailable, please check the logs or contact the administrator" is shown on the webclient. PC-clients don't sync that directory any more.

[magentaco]

I did not find associated information in the logs, however, after applying #8177 it works as expected and the share_folder contains shared files and syncs again with all clients.
In my environment this helped on v12.0.5 and v13.0.0

Changes to lib/private/Files/Cache/Wrapper/CacheJail.php
*/
public function getPathById($id) {
$path = $this->getCache()->getPathById($id);
*+ if ($path === null) {
*+ return null;
*+ }
*+
return $this->getJailedPath($path);
}

[MorrisJobke]

Duplicate of #8047