RTP/PS: fix crash at exit

(Rtp)Add then MuxAdd, so MuxDel before (Rtp)Del. Indeed, the PS muxer
sends packets when it's deleted, so the RTP stream is still needed.
(cherry picked from commit 816f5573)

modules/stream_out/rtp.c

@@ -566,10 +566,11 @@ static void Close( vlc_object_t * p_this )
     if( p_sys->p_mux )
     {
         assert( p_sys->i_es == 1 );
-        Del( p_stream, p_sys->es[0] );
 
         sout_MuxDelete( p_sys->p_mux );
+        Del( p_stream, p_sys->es[0] );
         sout_AccessOutDelete( p_sys->p_grab );
+
         if( p_sys->packet )
         {
             block_Release( p_sys->packet );