fixed minor regression

lib/single-file/single-file-browser.js

@@ -18,15 +18,18 @@
  *   along with SingleFile.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* global SingleFileCore, base64, DOMParser, getComputedStyle, TextDecoder, fetch, parseSrcset, uglifycss */
+/* global SingleFileCore, base64, DOMParser, getComputedStyle, TextDecoder, fetch, superFetch, parseSrcset, uglifycss */
 
 this.SingleFile = (() => {
 
+
 	// --------
 	// Download
 	// --------
 	const USER_AGENT = "Mozilla/5.0 (compatible; SingleFile Bot/1.0)";
 
+	let fetchResource;
+
 	class Download {
 		static async getContent(resourceURL, asDataURI) {
 			const requestOptions = {
@@ -36,8 +39,11 @@ this.SingleFile = (() => {
 				}
 			};
 			let resourceContent;
+			if (!fetchResource) {
+				fetchResource = typeof superFetch == "undefined" ? fetch : superFetch;
+			}
 			try {
-				resourceContent = await (this.superFetch || fetch)(resourceURL, requestOptions);
+				resourceContent = await fetchResource(resourceURL, requestOptions);
 			} catch (e) {
 				return asDataURI ? "data:base64," : "";
 			}