Fix the Memdisk/WIMBOOT mode/... tip message display error

When VTOY_DEFAULT_IMAGE was set to F6>xxxx, if you press F1 or ctrl+w, the tip message will show ??

INSTALL/grub/grub.cfg

@@ -1977,6 +1977,12 @@ export vtoy_efi_part
 export VENTOY_VERSION
 export VTOY_CUR_VIDEO_MODE
 export VTOY_EFI_ARCH
+export VTOY_MEM_DISK_STR
+export VTOY_ISO_RAW_STR
+export VTOY_GRUB2_MODE_STR
+export VTOY_WIMBOOT_MODE_STR
+export VTOY_ISO_UEFI_DRV_STR
+
 
 #special VTOY_DEFAULT_IMAGE process
 if [ -n "$VTOY_DEFAULT_IMAGE" ]; then