Events widget form can be submitted when empty or contains just spaces

[afercia]

In order to improve the user experience and reduce the requests sent to the API, it would be great to consider introducing a simple check to avoid the events widget form can be submitted when the form field is empty.

To reproduce what happens now:

• open the form to change location
• make sure the form field is empty and submit: the form gets submitted (it uses the last location?)
• repeat inserting just spaces in the form field and submit: the form gets submitted

[afercia]

40816.diff​ returns early if the search field is empty or contained only spaces.

[iandunn]

I don't think I'll have time to test 40816.diff​, but I looked at the diff and it sounds good to me.

[afercia]

Thanks @iandunn! Just noticed a typo feild > field, will fix during commit.

[afercia]

In 40799:

Dashboard: Don't trigger an Events search when the search field is empty.

Fixes #40816.