TRADE_ACTION_SLTP when TP or SL is 0

[Narek Kamalyan]

Trying to modify the order, need to modify only SL, position doesnt have TP.

Using this structure but getting error 0. Whats wrong. 

                           request.action    = TRADE_ACTION_SLTP;
                           request.symbol    = _Symbol;
                           request.sl        = new_sl;
                           request.tp        = 0;
                           request.position  = ticket;
                           request.magic     = MyMagic;