let qi::path::listData tolerate non-existing dirs

fix #14122

Change-Id: I79acccbb542f257226f35eae094e368e11589953
Reviewed-on: http://gerrit.aldebaran.lan:8080/19213
Reviewed-by: agarcia <agarcia@aldebaran-robotics.com>
Reviewed-by: gschweitzer <gschweitzer@aldebaran-robotics.com>
Reviewed-by: sbarthelemy <sbarthelemy@aldebaran-robotics.com>
Tested-by: sbarthelemy <sbarthelemy@aldebaran-robotics.com>