Add no results found on empty civireports dashlet

I've had a customer report that the dashlets are borked post upgrade. We are using shoreditch & I am investigating this issue https://github.com/civicrm/org.civicrm.shoreditch/issues/484

However in the context of grenwich I have noticed 2 things - the first of which is this issue - notably that part of the user's confusion was the blank box.

This box is blank in 5.30 and in dmaster (per below) so it is not new but I think we should have some indicator of lack of results rather than empty