Feedback for no search results should be negative

[LeandraH]

Is your feature request related to a problem? Please describe.
When sending feedback for a search request, we hide the buttons to chose if it's positive or negative feedback. The feedback that is sent to the CMS is neutral. I think it would make sense to have the feedback be automatically negative if no results were found.

Describe the solution you'd like
When no results were found, the feedback that is sent to the CMS should be negative.

Describe alternatives you've considered
We could leave it as neutral feedback since nobody has complained about it so far.

Additional context
Discussed in #3004 (comment)
One thing to note is that we use the feedback being null as opposed to negative for checking in some cases if the feedback can be sent but I think the current tests cover those cases.