Fix the path shown for unrepresented files

To represent the bunch of smaller files, we add a fake File item with a custom string as a file name.

Set the directory path too into that string. Otherwise, File adds the current working directory as the path for our fake item, showing the wrong information.

This example is scanning the .steam folder, but filelight is launched from build/filelight:

BEFORE	AFTER

BUG: 461964 FIXED-IN: 22.12.0