crate::font::load_layers and LayerSet::load should agree whether layercontents.plist is required or not

[madig]

norad/src/font.rs

Lines 640 to 642 in d4af02b

	if meta.format_version == FormatVersion::V3 && !layercontents_path.exists() {
	return Err(Error::MissingFile(layercontents_path.display().to_string()));
	}

vs.

norad/src/layer.rs

Lines 45 to 50 in d4af02b

	let to_load: Vec<(LayerName, PathBuf)> = if layer_contents_path.exists() {
	plist::from_file(&layer_contents_path)
	.map_err(|source| Error::PlistLoad { path: layer_contents_path, source })?
	} else {
	vec![(Arc::from(DEFAULT_LAYER_NAME), PathBuf::from(DEFAULT_GLYPHS_DIRNAME))]
	};

considering LayerSet::load is public.

[madig]

It's not public anymore, so maybe this is less important currently.