使用rqdata下载数据，经常出现如下问题：
反复下载失败几次后，也有时候会成功
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23:33:13 初始化CTA回测引擎
23:33:13 策略文件加载完成
23:33:13 RQData数据接口初始化成功
23:33:15 ----------------------------------------
23:33:15 IF88.CFFEX-1m开始下载历史数据
23:33:15 数据下载失败，触发异常：
Traceback (most recent call last):
File "D:\stock\vnpy\vnpy\app\cta_backtester\engine.py", line 365, in run_downloading
data = rqdata_client.query_history(req)
File "D:\stock\vnpy\vnpy\trader\rqdata.py", line 132, in query_history
adjust_type="none"
File "D:\ProgramData\Anaconda37\lib\site-packages\rqdatac\decorators.py", line 131, in wrap
return func(*args, **kwargs)
File "D:\ProgramData\Anaconda37\lib\site-packages\rqdatac\services\get_price.py", line 146, in get_price
raise PermissionDenied("Not permit to get minbar price ")
rqdatac.share.errors.PermissionDenied: Not permit to get minbar price
23:33:21 ----------------------------------------
23:33:21 IF88.CFFEX-1m开始下载历史数据
23:33:22 数据下载失败，触发异常：
Traceback (most recent call last):
File "D:\stock\vnpy\vnpy\app\cta_backtester\engine.py", line 365, in run_downloading
data = rqdata_client.query_history(req)
File "D:\stock\vnpy\vnpy\trader\rqdata.py", line 132, in query_history
adjust_type="none"
File "D:\ProgramData\Anaconda37\lib\site-packages\rqdatac\decorators.py", line 131, in wrap
return func(*args, **kwargs)
File "D:\ProgramData\Anaconda37\lib\site-packages\rqdatac\services\get_price.py", line 146, in get_price
raise PermissionDenied("Not permit to get minbar price ")
rqdatac.share.errors.PermissionDenied: Not permit to get minbar price
