Check whether all data in eContent has been consumed

Check whether all data in eContent has been consumed

It is possible that a given ASN.1 template generated d2i_*() function
didn't consume all data, so there is a potential for malleability.
The econtent is a sequence (which means it could be the concatenation
of several DER "blobs"). d2i_*() would only deserialize the first one
and not notice blobs following it.

OK tb@