message: Fix partially filled existing order
  Fix problem when a matching results in a partially filled existing order, the existing order and the bidder/ asker balance are not updated properly.
diff: @@ -173,6 +173,8 @@ void apply_exchange_buy( buy_order order ) {
  }
  seller_account = get_account( lowest_ask.seller.name );
  } else {
  + asks::update( lowest_ask );
  + save( seller_account );
  break; // buyer's bid should be filled
  }
  }
  @@ -234,6 +236,8 @@ void apply_exchange_sell( sell_order order ) {
  }
  buyer_account = get_account( highest_bid.buyer.name );
  } else {
  + bids::update( highest_bid );
  + save( buyer_account );
  break; // buyer's bid should be filled
  }
  }
  