fix issue when processing SVG sprites

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

@@ -316,7 +316,7 @@ class BatchRequest {
 		this.duplicates = new Map();
 	}
 
-	addURL(resourceURL, { asBinary, expectedType, groupDuplicates, baseURI, blockMixedContent }) {
+	addURL(resourceURL, { asBinary, expectedType, groupDuplicates, baseURI, blockMixedContent } = {}) {
 		return new Promise((resolve, reject) => {
 			const requestKey = JSON.stringify([resourceURL, asBinary, expectedType, baseURI, blockMixedContent]);
 			let resourceRequests = this.requests.get(requestKey);