sout: only wait all ES if muxer can't add tracks in any point

src/stream_output/stream_output.c

@@ -558,7 +558,7 @@ int sout_MuxGetStream( sout_mux_t *p_mux, unsigned i_blocks, mtime_t *pi_dts )
         sout_input_t *p_input = p_mux->pp_inputs[i];
         block_t *p_data;
 
-        if( block_FifoCount( p_input->p_fifo ) < i_blocks )
+        if( (!p_mux->b_add_stream_any_time) && block_FifoCount( p_input->p_fifo ) < i_blocks )
         {
             if( p_input->p_fmt->i_cat != SPU_ES )
             {