[Bug] Rendering an empty animation with the GIF encoder may prompt webcam image captures.

[chrisgervang]

Describe the bug
When hubble.gl is only partially integrated there is an edge case that can cause a developers webcam to be captured and saved onto their local machine. The data never leaves their local computer, and the web browser prompts the developer for permission before the webcam is active. That said, we don't want this occurring so we should fix this issue.

To Reproduce
We believe this issue occurs as default behavior of gifshot when there aren't any image frames passed in: https://github.com/yahoo/gifshot/blob/master/src/gifshot.js#L2733-L2765

Steps to reproduce the behavior:

const encoder = new GifEncoder();
encoder.start();
// no calls to encoder.add(), so no frames.
encoder.end();
// browser prompts for webcam permission
encoder.save();

Expected behavior
Hubble should use gifshot such that it never will capture from webcam.

Screenshots
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Desktop (please complete the following information):

• OS: Mac
• Browser Chrome

Additional context
Add any other context about the problem here.