Searchbox can be closed and disappears despite searchOpen: true

Following this showcase: https://codesandbox.io/s/muidatatables-misc-requests-4vkxk

When you set both:
```
search: false,
searchOpen: true,
```
The searchbox is open (always, as it seems...) and the search icon is disabled: this is to meet our user's requirement i.e. always have a search box.

However:
- searchbox CAN be closed; it shouldn't, as there is NO way to re-enable it.
- searchbox IS closed when you click either on View Columns or Filter Table icons (doesn't happen if you click on Download or Print) - already reported here https://github.com/gregnb/mui-datatables/issues/1203