Generates empty `svg.js` about ember-inline-svg

[buschtoens]

This is the .svg that produced the error: https://gist.github.com/buschtoens/4b82243b955eb8e0b1cc

As it turns out, I accidentally malformatted the file (line 17). ember-inline-svg should throw a descriptive error in this case and not silently insert an undefined.

[rlivsey]

Good catch, if svgo fails to optimize then I agree we should fail loudly with an informative error.

I was thinking we could fall back to the original unoptimized SVG, but that would just mask the problem so the error is a better idea.

[buschtoens]

So far I got Broccoli to throw a descriptive error and everything - in theory.

broccoli-spelunk seems to not support Promises, effectively destroying any error handling. If I remove flattenFolder from the pipeline, I get the expected Errors. With flattenFolder however, the build just stalls and runs forever.

[buschtoens]

I see you've written broccoli-concat. It should be possible to fork it and make it do what spelunk is supposed to do.

Your plugin supports Promises.

[buschtoens]

I'm modding broccoli-json-concat.

[buschtoens]

Got it working. I'll release a new npm package and submit the PR.