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

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.