hw/uefi: add missing uefi_str_is_valid check to uefi_vars_mm_lock_variable Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4213 Reviewed-by: Luigi Leonardi <leonardi@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Message-ID: <20260916145050.1329206-1-kraxel@redhat.com> (cherry picked from commit ff96d562906644699c6a553c35e6cd51383c26c2) Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>