iOS 拉流时， demo 中代码 频繁复现 只有声音没有画面

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如标题所述，iOS demo 中 rtmp 拉流时， 频繁出现 只有声音没有画面的问题。日志输出如下：
17:02:00 [💙] onStatisticsUpdate width = 0, height =0, fps = 0, videoBitrate = 0, audioBitrate = 16718
17:02:01 [💙] onStatisticsUpdate width = 0, height =0, fps = 0, videoBitrate = 0, audioBitrate = 17137
17:02:02 [💙] onStatisticsUpdate width = 0, height =0, fps = 0, videoBitrate = 0, audioBitrate = 16718
17:02:03 [💙] onStatisticsUpdate width = 0, height =0, fps = 0, videoBitrate = 0, audioBitrate = 7105
17:02:04 [💙] onAudioPlayStatusUpdate status = 1 reason = 2
17:02:04 [💙] onVideoPlayStatusUpdate status = 1, reason = 2