Error thrown if a combined css file does not exist

[fraddski]

amphora-html throws an error if the combined css file for a site does not exist and pages do not render. E.g. if combined-vulture.css is not present, pages on Vulture will not render.

CSS files should be optional.

[pfeytser]

Log if something from resolveMedia doesn't exist.

[nelsonpecora]

I believe all css files are optional, but let's verify this.

[TTaitFoster]

Is this still an issue?