Skip GRUB config if user supplies empty response

gentoostrap.sh

@@ -320,6 +320,10 @@ build-gentoo-chroot() {
 build-bootloader() {
 	# Last few chroot steps, mostly involving GRUB
 	read -p "Enter device to install GRUB to: " grubdev
+	if [ -z "$grubdev" ]; then
+		log "Skipping"
+		return 0
+	fi
 	log "Configuring GRUB"
 	[ -f /boot/grub ] && rm /boot/grub -f
 	[ -d /boot/grub ] || mkdir /boot/grub -p