Don't show "Welcome to GitLab" when the search didn't return any projects

Fixes #13785. /cc @pixdrift

### Before

![Screen_Shot_2016-03-02_at_10.55.02](/uploads/b6b6ead2143d01e374ad296e72182d79/Screen_Shot_2016-03-02_at_10.55.02.png)

### After

![Screen_Shot_2016-03-02_at_12.12.33](/uploads/6e16c44e69039c534ea0fc3373c6060b/Screen_Shot_2016-03-02_at_12.12.33.png)

See merge request !3059