[BUGFIX] Support additional checkboxes in email4link lightbox

Before this commit values of additional checkboxes (e.g. registration for newsletter) were sent every time an email4link popup was submitted even if the checkbox was not checked.

Related: https://projekte.in2code.de/issues/65254

Resources/Private/Build/JavaScript/Frontend/Lux.js

@@ -968,15 +968,13 @@ function LuxMain() {
     var target = link.getAttribute('target');
     var sendEmail = link.getAttribute('data-lux-email4link-sendemail') || 'false';
 
-    var formArguments = {};
     var form = that.lightboxInstance.element().querySelector('[data-lux-email4link="form"]');
-    for (var i = 0; i < form.elements.length; i++) {
-      var field = form.elements[i];
-      var name = field.getAttribute('name');
-      if (name !== null && name.indexOf('email4link[') !== -1) {
-        var value = field.value;
-        var nameParts = name.split('[');
-        name = nameParts[1].substring(0, nameParts[1].length - 1);
+    var formData = new FormData(form);
+    var formArguments = {};
+
+    for (var [key, value] of formData.entries()) {
+      if (key.startsWith('email4link[')) {
+        var name = key.split('[')[1].split(']')[0];
         formArguments[name] = value;
       }
     }