stream: don't leak stats structure
stream: don't leak stats structure

Don't leak the stats structure and deal with NULL stats.

barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,thaytan/gst-rtsp-server,barisdemiray/gst-rtsp-server,surround-io/gst-rtsp-server,hsteinhaus/gst-rtsp-server,barisdemiray/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,hsteinhaus/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,thaytan/gst-rtsp-server