Fail fast on invalid cbc payload length
Fail fast on invalid cbc payload length

This value is used for mac updates. An obviously incorrect payload
length will fail in composite CBC decrypt. Let's catch it sooner.

colmmacc/s2n,bpdavidson/s2n,raycoll/s2n,awslabs/s2n,wcs1only/s2n,jldodds/s2n,gibson-compsci/s2n,colmmacc/s2n,wcs1only/s2n,gibson-compsci/s2n,colmmacc/s2n,PKRoma/s2n,raycoll/s2n,wcs1only/s2n,raycoll/s2n,raycoll/s2n,colmmacc/s2n,bpdavidson/s2n,bpdavidson/s2n,bpdavidson/s2n,jldodds/s2n,gibson-compsci/s2n,PKRoma/s2n,gibson-compsci/s2n,alexeblee/s2n,alexeblee/s2n,PKRoma/s2n,PKRoma/s2n,wcs1only/s2n,wcs1only/s2n,awslabs/s2n,PKRoma/s2n,awslabs/s2n,raycoll/s2n,awslabs/s2n,colmmacc/s2n,gibson-compsci/s2n,jldodds/s2n,PKRoma/s2n,wcs1only/s2n,alexeblee/s2n,awslabs/s2n,alexeblee/s2n,alexeblee/s2n,bpdavidson/s2n,gibson-compsci/s2n,jldodds/s2n,raycoll/s2n,awslabs/s2n,jldodds/s2n,alexeblee/s2n,bpdavidson/s2n,PKRoma/s2n,wcs1only/s2n,wcs1only/s2n,PKRoma/s2n,colmmacc/s2n