Empty SVGs are not being downloaded

[SushiRoll53]

Describe the bug

Figma has some interesting capabilities, one of them is being able to generate empty vectors. Parabeac-core takes all vectors & download them as svgs, but if the vector happen to be empty, Parabeac-core cannot download it. But the issue comes when it tries to still use & export that svg on the files, the pubspec.yaml for example, complains about missing assets.
I believe, core should detect the empty svg, that was not exported & then let the rest of core know, to not use it, since it will not be exported.

To Reproduce

Steps to reproduce the behavior:

1. Convert Figma file https://www.figma.com/file/WyKbF0awxlRmAIJ9JP4YvR/FYTR-Parabeac-Build?node-id=843%3A1829
2. On the output, look for the svg asset, states.svg
3. It should not be there, but if we look on the pubspec.yaml we will see, that it is part of the package

Impact of the problem

In case of multiple empty vectors, it will generate a lot of not necessary lines.

Environment:

• OS: macOS