fixed url validation test

lib/single-file/single-file-core.js

@@ -1302,7 +1302,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 		}
 
 		static testValidURL(resourceURL, baseURI) {
-			return DomUtil.testValidPath(resourceURL, baseURI) && (resourceURL.match(HTTP_URI_PREFIX) || resourceURL.match(FILE_URI_PREFIX)) && !resourceURL.match(NOT_EMPTY_URL);
+			return DomUtil.testValidPath(resourceURL, baseURI) && (resourceURL.match(HTTP_URI_PREFIX) || resourceURL.match(FILE_URI_PREFIX)) && resourceURL.match(NOT_EMPTY_URL);
 		}
 
 		static matchImport(stylesheetContent) {