修复拉流代理获取流信息可能访问空指针的bug

此bug由 #2448 引入，触发条件：
- 1.配置文件rtsp.directProxy设置为0
- 2.调用addStreamProxy代理rtsp流

在非直接代理情况下，PlayerProxy::_media_src为空，导致访问空指针。

src/Player/PlayerProxy.cpp

@@ -65,8 +65,8 @@ void PlayerProxy::setOnConnect(std::function<void(const TranslationInfo&)> cb) {
 
 void PlayerProxy::setTranslationInfo()
 {
-    _transtalion_info.byte_speed = _media_src->getBytesSpeed();
-    _transtalion_info.start_time_stamp = _media_src->getCreateStamp();
+    _transtalion_info.byte_speed = _media_src ? _media_src->getBytesSpeed() : -1;
+    _transtalion_info.start_time_stamp = _media_src ? _media_src->getCreateStamp() : 0;
     _transtalion_info.stream_info.clear();
     auto tracks = _muxer->getTracks();
     for (auto &track : tracks) {