don't replace 4xx with empty contents

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

@@ -69,9 +69,6 @@ this.SingleFile = this.SingleFile || (() => {
 			} catch (error) {
 				return options && options.asDataURI ? "data:base64," : "";
 			}
-			if (resourceContent.status >= 400) {
-				return options && options.asDataURI ? "data:base64," : "";
-			}
 			let contentType = resourceContent.headers && resourceContent.headers.get("content-type");
 			let charSet;
 			if (contentType) {