Gstreamer/Deepstream 多输入源输入，打开失败源判断
当使用uridecodebin插件打开多输入源时，发现在打开任一源失败时，在消息监听回调会返回GST_MESSAGE_ERROR错误消息从而退出管道，详细错误信息是gstrtspsrc.c(7469): gst_rtspsrc_retrieve_sdp (): /GstPipeline:StreamTogetherProcess/GstBin:decode-bin-1/GstURIDecodeBin:uri-decode-bin1/GstRTSPSrc:source:Failed to conn
