D5257: manifest: also reject obviously-too-short lines when parsing lines

[Yuya Nishihara]

> +		if ((next - data) < 22) {
> +			/* We should have at least 22 bytes in a line:
> +			   1 byte filename
> +			   1 NUL
> +			   20 bytes of hash

Queued, but I think it should be **40** bytes of hexadecimal hash.