fixed rtp with mux=ts

modules/stream_out/rtp.c

@@ -397,7 +397,7 @@ static int Open( vlc_object_t *p_this )
         sout_access_out_t *p_grab;
         char *psz_rtpmap, url[NI_MAXHOST + 8], access[17], psz_ttl[5], ipv;
 
-        if( p_sys->psz_destination )
+        if( !p_sys->psz_destination || *p_sys->psz_destination == '\0' )
         {
             msg_Err( p_stream, "rtp needs a destination when muxing" );
             free( p_sys );