imageless spectrum graph doesn't undim if there are no tags

[jywarren]

https://spectralworkbench.org/spectrums/78144 undims, and has no image, but one tag;

https://spectralworkbench.org/spectrums/80038 also has no image, and does not undim, and has no tags.

I forked 80038 and got https://spectralworkbench.org/spectrums/82180, which immediately had a "forked" tag, and did undim successfully.

Maybe the undim is only run after tags, and when there aren't any, it never runs?

Undim is here: https://github.com/publiclab/spectral-workbench.js/blob/master/src/SpectralWorkbench.Graph.js#L77

run on graph.refresh_and_reload()

[jywarren]

Attempted a fix for this in v0.1.4, tested here: https://github.com/publiclab/spectral-workbench.js/blob/master/spec/javascripts/graph_spec.js#L88-L102 but test fails with opacity = '' instead of '1'... odd.