don't use original CSS test as fallback

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

@@ -119,7 +119,7 @@ this.cssMinifier = this.cssMinifier || (() => {
 				}
 			}
 		}
-		return (selectorText || cssRule.selectorText) + "{" + (styleCssText || cssRule.style.cssText) + "}";
+		return (selectorText || cssRule.selectorText) + "{" + styleCssText + "}";
 	}
 
 	function processStyleAttribute(cssStyle, mediaAllInfo) {