fix: external css - handle HTML5-compliant syntax

Author: Jakub Freisler

lib/process-style.js

@@ -52,7 +52,7 @@ function getPreprocessOptions(lang, filePath, jestConfig) {
 module.exports = function processStyle(stylePart, filePath, config = {}) {
   const vueJestConfig = getVueJestConfig(config)
 
-  if (stylePart.src && !stylePart.content) {
+  if (stylePart.src && !stylePart.content.trim()) {
     const cssFilePath = applyModuleNameMapper(
       stylePart.src,
       filePath,