Guest can't access shared files if a "share_folder" is set

[schiessle]

If the admin configures a default folder for shares in the config.php with the "share_folder" parameter guests can't access the shares.

My guess is the following: Guest have a quota zero by default. They are not allowed to create custom files or folders. This also prevent Nextcloud to created the folder specified in the "share_folder" setting and therefore the mount points for all shares are not accessible for the guest user

[schiessle]

subset of #1091