In cases where smb4php returns false of an empty array stat/( has to ret...

...urn false.

Fixes #3466 because the test method of external filesystems uses stat() to detect if the given parameters are okay.

Changes to 3rdparty are necessary as well:
https://github.com/owncloud/3rdparty/pull/33

@icewind1991 @MTGap THX