file_path to 0 for surety.
(grub_chainloader_boot): Set exit_data to NULL.
Unset the loader once done.
(grub_cmd_chainloader): Fix confusing error message if file is empty.
(devpath_1): Use MAKE_PIWG_PATH.
(devpath_2): Likewise.
(devpath_3): Likewise.
(devpath_4): Likewise.
(devpath_5): Likewise.
(devpath_6): Likewise.
The appleldr.mod was checked that to be binary identical to previous
version.