Fix the boot issue for Untangle ISO in legacy bios mode. (#1054)

INSTALL/grub/grub.cfg

@@ -961,6 +961,14 @@ function legacy_linux_menu_func {
             set ventoy_fs_probe=iso9660
             loopback loop "$1$2"
         fi
+
+        if [ -f (loop)/isolinux/isolinux.cfg ]; then
+            if vt_iso9660_isjoliet; then
+                vt_iso9660_nojoliet 1
+                loopback -d loop
+                loopback loop "$1$2"
+            fi
+        fi
     
         vt_load_cpio  $vtoy_path  "$2" "$1" "busybox=$ventoy_busybox_ver"