Fix displaying variable values on vertical line with VBO render

Follow-up of bacf5e14

src/render/vbo/Render_alternate.cpp

@@ -1263,8 +1263,11 @@ void Render_alternate::draw_vertical_line(){
 void Render_alternate::update_vertical_line(){
     if (_mouse_pressed_inside_container)
         set_vertical_line(0);
-    else
+    else {
         set_vertical_line(render_to_trace_x( screen_to_render_x(_mouse_x)));
+        Element_pos d = render_to_trace_x( screen_to_render_x(_mouse_x));
+        _core->launch_action(_core->_STATE_UPDATE_VARVALUES, &d);//update the value of the variables to display
+    }
     updateGL();
 }