Completion of empty directories

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

$ zsh -f
% mkdir xxx
% mv * x/<TAB>

When xxx/ is empty, the <TAB> does nothing.  Could it complete x/ to xxx/?

Using _complete_debug (on another example, xxx/f/ -> xxx/foo/ with
xxx/foo/ being empty) I see that xxx/foo/ _is_ getting matched against,
but I haven't been able to identify the point (in _path_files,
presumably) where it is checked that the directory is non-empty.