init position with loaded symbols

pkg/bbgo/environment.go

@@ -190,6 +190,8 @@ func (environ *Environment) Init(ctx context.Context) (err error) {
 
 		// trade sync and market data store depends on subscribed symbols so we have to do this here.
 		for symbol := range session.loadedSymbols {
+			session.positions[symbol] = &Position{Symbol: symbol}
+
 			var trades []types.Trade
 
 			if environ.TradeSync != nil {

pkg/bbgo/position.go

@@ -6,6 +6,7 @@ import (
 )
 
 type Position struct {
+	Symbol      string           `json:"symbol"`
 	Base        fixedpoint.Value `json:"base"`
 	Quote       fixedpoint.Value `json:"quote"`
 	AverageCost fixedpoint.Value `json:"averageCost"`