negative pLen

[bennetyee]

go-common/sivaessha2/symmetric.go

Line 111 in 02817f4

aadLen, pLen := len(additionalData), len(ciphertext)-TagSize

negative pLen when len(cipherText) < TagSize is checked by writeLenVec which is a bit weird since it's usually nice to check nearer where the possibly bad value is computed.

a comment on L170 on why aadLen < 0 check is not necessary (and remove the commented out check code) would be nice.