Builder should Error when font name in config doesn't match glyphs file

[aaronbell]

In converting Museo Moderno to the UFR format, I ran into an issue where the variable font was not generating instances in the fvar table. It turned out that the issue was that there was a slight mismatch between the font name in the config.yaml file ("Museo Moderno") and the name in the Glyphs file itself ("MuseoModerno").

I think that it would make sense to issue an error if there is mismatch between these two locations rather than building the font and silently failing to produce an fvar table.