[FTX] Fix OnGetOrderDetailsAsync (#676)

Author: bezysoftware

src/ExchangeSharp/API/Exchanges/FTX/ExchangeFTXAPI.cs

@@ -288,7 +288,7 @@ protected async override Task<ExchangeOrderBook> OnGetOrderBookAsync(string mark
 		/// <inheritdoc />
 		protected async override Task<ExchangeOrderResult> OnGetOrderDetailsAsync(string orderId, string marketSymbol = null, bool isClientOrderId = false)
 		{ // https://docs.ftx.com/#get-order-status and https://docs.ftx.com/#get-order-status-by-client-id
-			if (marketSymbol != null) throw new NotImplementedException("Searching by marketSymbol is either not implemented by or supported by this exchange. Please submit a PR if you are interested in this feature");
+			if (!string.IsNullOrEmpty(marketSymbol)) throw new NotImplementedException("Searching by marketSymbol is either not implemented by or supported by this exchange. Please submit a PR if you are interested in this feature");
 
 			var url = "/orders/";
 			if (isClientOrderId)
@@ -339,7 +339,6 @@ protected override async Task<ExchangeWithdrawalResponse> OnWithdrawAsync(Exchan
 				{ "coin", request.Currency },
 				{ "size", request.Amount },
 				{ "address", request.Address },
-				{ "tag", request.AddressTag },
 				{ "nonce", await GenerateNonceAsync() },
 				{ "password", request.Password },
 				{ "code", request.Code }