pathchk: check empty path by default

[Luv-Ray]

fix #5314
comment in GNU pathchk:

Check whether a file name component is in a directory that is not searchable, or has some other serious problem. POSIX does not allow "" as a file name, but some non-POSIX hosts do (as an alias for "."), so allow "" if lstat does.

I use std::fs::symlink_metadata, which currently corresponds to the lstat function on Unix and the GetFileInformationByHandle function on Windows instead.

It looks good in my local, but I don't have a non-POSIX environment, so it may need some more tests.
In my local:

$ ./target/debug/pathchk ""         
pathchk: '': No such file or directory

$ ./target/debug/pathchk "" ""      
pathchk: '': No such file or directory
pathchk: '': No such file or directory

[sylvestre]

please check the error message too :)

[Luv-Ray]

I have change no_stdout to stderr_only :)

[cakebaker]

Thanks :)