Fix Error Invalid Group Specifier Name on Safari by removing REGEX lookbehind group construct (fixes #239)

public/scripts/util.js

@@ -583,4 +583,14 @@ async function decodeBase64Text(base64) {
     if (!base64) throw new Error('Base64 is empty');
 
     return decodeURIComponent(escape(window.atob(base64)))
+}
+
+function isUrlValid(url) {
+    try {
+        let urlObj = new URL(url);
+        return true;
+    }
+    catch (e) {
+        return false;
+    }
 }