freeciv-proxy: Fill size of final encoded message to the message header
freeciv-proxy: Fill size of final encoded message to the message header

In messages sent to the freeciv server, length of the message to the
header was one from message before UTF-8 encoding, potentially wrong
one if encoding changes the length.

Signed-off-by: Marko Lindqvist <09de095ce3e68c59408f3e8a648405bbea619591@gmail.com>

tltneon/freeciv-web,andreasrosdal/freeciv-web,andreasrosdal/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,andreasrosdal/freeciv-web,andreasrosdal/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,adaxi/freeciv-web,andreasrosdal/freeciv-web,adaxi/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,tltneon/freeciv-web