Revert the changes made in commit 02910b7 to the mysql error packet
parsing, as it didn't take the CLIENT_PROTOCOL_41 case into account.
It appears that the non-CLIENT_PROTOCOL_41 case was off by one as well
(sliced data on 4 vs 3).
I also added two new tests to cover those cases.
See: https://dev.mysql.com/doc/internals/en/packet-ERR_Packet.html