Fix RPT Error. See details below

Referenced here: http://epochmod.com/forum/index.php?/topic/15679-rpt-error-when-buying-stuff/

Error

    19:28:05 "EPOCH SERVERTRADE: Player: ROCU[] (76561198046592472) bought a Unknown Vehicle in/at trader city Sabina for     <null>x <null>"
    19:28:05 Error in expression <urrency =    _this select 5;
    _qty =        _this select 6;
    _clientID =     owner _player;
    _p>
    19:28:05 Error position: <select 6;
    _clientID =     owner _player;
    _p>
    19:28:05 Error Zero divisor
    19:28:05 File z\addons\dayz_server\compile\server_tradeObject.sqf, line 9