Broken EFI grub.cfg on stretch images
Debian-installer testing gives GRUB prompt while booting on UEFI
platforms; the issue is related to a broken /boot/grub/grub.cfg file.
The screen shows only Debian's background and the loaded font but no
menu options are shown.
Up to the date (Nov 23), all three (official, weekly and daily) images
are broken. Its grub.cfg file is only 449 bytes and the last line is
"set theme="; there are no "menuentry" directives, so after loading
theme it comes with the prompt.