grub.cfg: optimize search_isolinux

GRUB is slow at device enumeration. This patch works around it in the same way
as vitali64's recent patch.

resources/grub/config/grub.cfg

@@ -77,16 +77,21 @@ function try_isolinux_config {
 	done
 }
 function search_isolinux {
-	unset ddev
+	for i in 0 1 2 3 4 5 6 7 8 9 10 11; do
-	if [ (${1}?) != "(${1}?)" ]; then
+		# TODO : Find a better way to detect how many partitions
-		ddev=(${1}*) # Both raw and partitioned devices.
+		#      : are on the disk instead of hardcoding.
-		echo -n "Attempting to parse isolinux menu from: "
+		echo "\nAttempting to parse isolinux menu from ${1}${i}"
-	fi
+		for part in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do
-	for i in ${ddev}; do
+			# MBR/GPT partitions
-		echo -n "${i} "
+			echo "\nTrying partiton ${part}"
-		try_isolinux_config "${i}"
+			try_isolinux_config "(${1}${i},${part})"
+		done
+		# raw devices
+		echo "\nTrying raw usb device ..."
+		try_isolinux_config "(${1}${i})"
+		echo # Insert newline
 	done
-	echo # Insert newline
+
 }
 menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o' {
 # GRUB2 handles (almost) every possible disk setup, but only the location of