GLUI_Main::mouse dead code?

[nigels-com]

@mick-p1982 notes that there is dead code in relation to AND 0 in GLUI_Main::mouse

      if ( active_control AND
           active_control->active_type == GLUI_CONTROL_ACTIVE_MOUSEDOWN AND 0)
      {
        /*** This is a control that needs to be deactivated when the
        mouse button is released ****/
        deactivate_current_control();
      }