Bug: `tag` is incorrectly extracted from `bundle` in `ShieldNote.decryptRandom`

[Robert-MacWha]

The tag occupies bytes 32-64 in bundle[0]. However, the code extracts 48 bytes from 16-64.

Note: This is currently non-breaking since AES.decryptGCM trims the incoming iv and tag with ByteUtils.trim. However it's incorrect and relies on side-effects of the utility code.

#125