Group Vulnerability Report: Fix misleading empty-state when a group has no vulnerabilities

The following discussion from !47861 (merged) should be addressed:

• @dpisek started a discussion: (+6 comments)

  @svedova : Anyways, I noticed the empty dashboard occurs when you have projects in your group but those projects have no vulnerabilities. The empty dashbaord message we displays seems confusing. It should probably say you have no vulnerabilities instead of add projects to your group.

Screenshot of Group Vulnerability Report for a group without reported vulnerabilities