[CORE] getting a client by its db id will return the existing client object if found in the list of connected clients

Should fix the issue that arise when a game require the player cid for the kick command and the admin issue the kick command with the @<dbid>
See http://forum.bigbrotherbot.net/arma-2/b3-not-kicking-player/msg39392/#msg39392
Merge branch 'release-1.10' of https://github.com/BigBrotherBot/big-brother-bot into release-1.10