Use the unjailed-path in OC_Helper::getStorageInfo() for files located in SharedStorage.

The current implementation already switches the storage-backend to
$storage->getSourceStorage(). However, it then calls
$rootInfo->getInternalPath() which returns the internal path relative to
the storage where the share is mounted. This is wrong, we need also to
unjail the path. Compare, e.g., with
OCA\Files_Sharing\SharedStorage::file_get/put_contents() for the
"logic".

Signed-off-by: Claus-Justus Heine <himself@claus-justus-heine.de>