Race condition on event handling. ex) pykiwoom.comm_rq_data

your code, pykiwoom.comm_rq_data has race condition. It leads entire program to dead-lock.

After calling following line :
`return_code = self.dynamicCall("CommRqData(QString, QString, int, QString)", request_name, tr_code, inquiry, screen_no)`

`receive_tr_data()` can be returned before calling `self.request_loop.exec_()`
then `self.request_loop.exec_()` won't return forever.