fixed unexpected font removal issue

lib/single-file/css-fonts-minifier.js

@@ -98,7 +98,12 @@ this.fontsMinifier = this.fontsMinifier || (() => {
 			if (variableFound) {
 				unusedFonts = [];
 			} else {
-				const filteredUsedFonts = new Set(usedFonts.map(fontNames => fontNames.find(fontName => declaredFonts.has(fontName))).filter(fontName => fontName));
+				const filteredUsedFonts = new Set();
+				usedFonts.forEach(fontNames => fontNames.forEach(fontName => {
+					if (declaredFonts.has(fontName)) {
+						filteredUsedFonts.add(fontName);
+					}
+				}));
 				unusedFonts = Array.from(declaredFonts).filter(fontFamilyName => !filteredUsedFonts.has(fontFamilyName));
 			}
 			doc.querySelectorAll("style").forEach(style => {