* Per https://en.wikipedia.org/wiki/Design_of_the_FAT_file_system#Directory_entry it
is possible to have a FAT directory entry with a 'EFI' volume label alongside with
a 'EFI' subdirectory.
* If that happens, then the current Syslinux libfat_searchdir() code may treat the
'EFI' volume label as an empty subdirectory and say that there are no bootloaders,
even if the 'EFI\Boot\Boot###.efi' binaries really do exist.
* Fix this by filtering out entries with the 'volume label' attribute (0x08).
* For good measure, also filter out entries with the 'device' attribute (0x40), as
it is technically possible to create a 'EFI' device leading to the same issue.
* Closes#2288.
* Closes#2289.