[stable6] Fixed missing files on SMB storage

Files with attribute "N" weren't parsed out of the file list returned by
smbclient. It seems that these files appear when created on a Linux SMB
mount directly and that have no executable bit.

@icewind1991 for some reason it seems we missed fixing this on stable6 / stable5.

Please review @karlitschek @icewind1991 @schiesbn