改进云端下载数据稳定性

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https://ld246.com/article/1656424989444

对于下载报错 http2: server sent GOAWAY and closed the connection; LastStreamID=1999, ErrCode=NO_ERROR, debug="" 不认为是错误，应该进行请求重试而不是直接返回报错。

• https://stackoverflow.com/questions/45209168/http2-server-sent-goaway-and-closed-the-connection-laststreamid-1999
• https://stackoverflow.com/questions/41592929/aws-alb-http-2-and-goaway
• x/net/http2: make Transport return nicer error when Amazon ALB hangs up mid-response? golang/go#18639

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已经做过重试请求了……这问题看来暂时无法解决，先关闭了。