Merge pull request #10149 from owncloud/storage-wrapper-check

Check result of storage wrappers

lib/private/files/storage/storagefactory.php

@@ -99,6 +99,9 @@ class StorageFactory implements IStorageFactory {
 		}, $wrappers);
 		foreach ($wrappers as $wrapper) {
 			$storage = $wrapper($mountPoint->getMountPoint(), $storage, $mountPoint);
+			if (!($storage instanceof \OCP\Files\Storage)) {
+				throw new \Exception('Invalid result from storage wrapper');
+			}
 		}
 		return $storage;
 	}