Visual output tab label is wonky on projects without visual output

[patch0]

In main, we noticed that for projects with non-visual components, rather than disappearing the Visual output tab it becomes wonky.

e.g.

https://projects.raspberrypi.org/en/projects/editor-hello-world/editor

vs

https://staging-projects.raspberrypi.org/en/projects/editor-hello-world/editor

I think this only affects projects with no visible libraries present, i.e. ones where the "visible output" tab shouldn't be shown on load.

This was tweaked in #1203, which hid the split output button correctly, but didn't quite hide the visual output button.

(Also I've set my default font to a monospace one so I can easily see where the default font isn't being set correctly! So don't worry about the button styling etc.)

[patch0]

This issue is blocking us upgrading the editor on the projects site, which means content authors can't make use of Pyodide.

(see slack thread)