Avoid displaying empty list of projects ("Trending")

Description

When clicking "Explore projects", display "Most stars" or "All" instead of "Trending", when there are no trending projects.

Proposal

My proposal is, to display the "All" page, or maybe "Most stars" in case there are no "Trending" projects.

Links / references

Documentation blurb

Overview

When you want to explore projects, and for some reason, there are no trending projects, it is always one extra moment "Huh?" and then an extra click ("All") to really explore the projects.

I don't know how "Trending" projects are calculated, but for us, the "Trending" page is always empty.

Use cases

It's for any user wanting to explore projects. This might make more sense for company/private GitLab instances than public-hosted instances.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.