Fix(auto_trader): casue panic because close a close channel (#737)

Co-authored-by: zbhan <zbhan@freewheel.tv>

trader/auto_trader.go

@@ -269,6 +269,9 @@ func (at *AutoTrader) Run() error {
 
 // Stop 停止自动交易
 func (at *AutoTrader) Stop() {
+	if !at.isRunning {
+		return
+	}
 	at.isRunning = false
 	close(at.stopMonitorCh) // 通知监控goroutine停止
 	at.monitorWg.Wait()     // 等待监控goroutine结束