Description of problem:
If the user accidentally deselects the project-version from the list in a request to join group action, the resul is a mere notification on the project languages list

Version-Release number of selected component (if applicable):
3.3.0 RC1

How reproducible:
Easy always

Steps to Reproduce:
1. Sign in as a project maintainer
2. Go to a project version, click the Request to add project to group
3. Select any group
4. Deselect the item in the list at the top of the page
5. Press Send Message

Actual results:
Goes back to the project version page, with "No project version selected." at the top

Expected results:
Should be on the same request page, with an appropriate error.

Additional info: