Fix black first frame when rendering gifs in setup

[davepagurek]

Resolves #6080

Changes

• Previously, the first frame of a gif rendered in setup would be black
• This looks like it's because we hide canvases until setup finishes, and that seems to be affecting our ability to grab pixels
• Awaits an immediately-resolving promise before starting to render frames defers execution so that setup completes before we pick back up again

Screenshots of the change

Before: the downloaded gif starts on a black frame

After: the first frame has content!

Working gif, for reference:

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated