修复MediaSource::close线程安全问题

主动或无人观看关闭流可能会由于线程安全问题导致崩溃

src/Rtsp/RtspSession.cpp

@@ -1175,9 +1175,7 @@ int RtspSession::getTrackIndexByInterleaved(int interleaved) {
 }
 
 bool RtspSession::close(MediaSource &sender) {
-    //此回调在其他线程触发
-    string err = StrPrinter << "close media: " << sender.getUrl();
-    safeShutdown(SockException(Err_shutdown,err));
+    shutdown(SockException(Err_shutdown,"close media: " + sender.getUrl()));
     return true;
 }