Hide Folders tab when no topics available on channel page

[nucleogenesis]

Summary

The Folders tab was showing because [] == true so I added some .length checks to the display logic there.

The issue reports that the problem was that the Folders tab had a worthless "View more" link shown, but I think that the pointless empty tab needed hidden as well.

References

Fixes #8701

Reviewer guidance

Do channels like the example one in #8701 have the Folders tab?

Do channels like Kolibri QA Channel (which has folders) show the tab properly?

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