rtsp: fix socket leak

A socket is leaked when the client passes a wrong session identifier.
A remote attacker could craft malicious RTSP requests and...
(cherry picked from commit eea1cddc)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>

modules/stream_out/rtsp.c

@@ -596,6 +596,7 @@ static int RtspHandler( rtsp_stream_t *rtsp, rtsp_stream_id_t *id,
                         {
                             answer->i_status = 454;
                             vlc_mutex_unlock( &rtsp->lock );
+                            net_Close( track.fd );
                             continue;
                         }
                     }