Found a situation where grid vports was reporting rows/cols values when that vport was set to `none`.

Test situation:
- with all grid vports set to none, attach grid.
- remove grid and set vport 1 back to none
- `tab.print(grid.vports[1])` then returns the following:

```
cols	16
name	none
all	function: 0x1f79248
led	function: 0x1f6bd98
rows	8
refresh	function: 0x1fa7e60
intensity	function: 0x1fa8548
rotation	function: 0x1fa8590
```
Thus `name` is set to none, but `rows` and `cols` are not reset to zero

Can also be tested with my Grid Test script in the lines Library when manually changing grid port positions.

Proposed fix: reset rows/cols to zero in Grid.update_devices()