boot: reject GPT headers with SizeOfPartitionEntry below the minimum

boot: reject GPT headers with SizeOfPartitionEntry below the minimum

Commit 0cf5f816f22c replaced the original lower-bound check

    if (h->SizeOfPartitionEntry < sizeof(EFI_PARTITION_ENTRY))
            return false;

with a multiple-of check

    if ((h->SizeOfPartitionEntry % sizeof(EFI_PARTITION_ENTRY)) != 0)
            return false;

to additionally require the entry size to be a multiple of 128. The
modulo test is however also satisfied by SizeOfPartitionEntry == 0, so a
GPT header advertising a zero entry size now passes verify_gpt().

Restore the lower bound in addition to the multiple-of check, so the
entry size must be at least sizeof(EFI_PARTITION_ENTRY) and a multiple of
it (128 bytes).

Follow-up for 0cf5f816f22c78740e122dfb6b3942ba4241717b