asf.c: write new header when track is removed/added

modules/mux/asf.c

@@ -641,6 +641,9 @@ static int AddStream( sout_mux_t *p_mux, sout_input_t *p_input )
     vlc_array_append( p_sys->p_tracks, (void *)tk);
     tk->i_id = vlc_array_index_of_item( p_sys->p_tracks, tk ) + 1;
 
+
+    p_sys->b_write_header = true;
+
     return VLC_SUCCESS;
 }
 
@@ -674,6 +677,8 @@ static int DelStream( sout_mux_t *p_mux, sout_input_t *p_input )
 
     vlc_array_remove( p_sys->p_tracks, vlc_array_index_of_item( p_sys->p_tracks, (void *)tk ) );
 
+
+    p_sys->b_write_header = true;
     return VLC_SUCCESS;
 }