The client's UI makes it easy to submit invalid dates not supported by
LocalDate. Rather than throwing an exception in a codec, it'd be good to
support representing these for:
* Allowing the development of a debugging proxy server that sits between
the client and game server.
* Making it easier to send the invalid date of birth response to the
creation request.
We'll still switch to LocalDate as early as possible in the packet
handler in the future.
Signed-off-by: Graham <gpe@openrs2.org>