fixing small bug in grid_container when placeholder 'None' components were being added
fixing small bug in grid_container when placeholder 'None' components were being added

tommy-u/chaco,burnpanck/chaco,burnpanck/chaco,ContinuumIO/chaco,ContinuumIO/chaco,ContinuumIO/chaco,burnpanck/chaco,tommy-u/chaco,ContinuumIO/chaco,tommy-u/chaco