Empty replies can be sent to forum posts through the dashboard

Summary

On the dashboard, you can just press enter in the answer field on any forum post without writing anything, essentially submitting an empty reply to that post.

Steps to reproduce

• Go to the dashboard
• Click on "Schreibe eine Antwort" on any forum post and hit enter
• (ideally, delete the empty reply afterwards)

What is the current bug behavior?

An empty reply gets added to the forum post

What is the expected correct behavior?

A reply should always contain something, so the empty reply should not get sent.

Possible fixes

https://gitlab.com/foodsharing-dev/foodsharing/-/blob/master/src/Modules/Dashboard/components/ActivityPost.vue#L193 is missing a check for empty strings