The issue is that when using locale compare to compare the filenames, we turn the numeric option to on, so that "1" < "2" < "10". This was done so that we get Undefined-1, Undefined-2, Undefined-3, Undefined-10, instead of Undefined-1, Undefined-10, Undefined-2, Undefined-3. But this break the file sorting, since we preppend a 0 to folders and a 1 to files. So later we have that "1XX" < "002", where the first is a file and the second a folder. By changing the prefixes to letters, we can fix this.

This is for #8273.