remove empty @media rules

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

@@ -67,6 +67,9 @@ this.cssRulesMinifier = this.cssRulesMinifier || (() => {
 			if (cssRuleData.type == "Atrule" && cssRuleData.name == "media" && cssRuleData.block && cssRuleData.prelude) {
 				const mediaText = cssTree.generate(cssRuleData.prelude);
 				processRules(cssRuleData.block.children, sheetIndex, mediaInfo.medias.get("rule-" + sheetIndex + "-" + mediaRuleIndex + "-" + mediaText));
+				if (!cssRuleData.prelude.children.getSize() || !cssRuleData.block.children.getSize()) {
+					removedCssRules.push(cssRule);
+				}
 				mediaRuleIndex++;
 			} else if (cssRuleData.type == "Rule") {
 				const ruleInfo = mediaInfo.rules.get(cssRuleData);