Handles the case of closed registrations

lib/ui/widgets/group_membership_widget.dart

@@ -132,6 +132,11 @@ class _GroupMembershipWidgetState extends SafeState<GroupMembershipWidget> {
 
   /// Build visitor state
   Widget _buildVisitorState() {
+
+    // Check if the user can request membership
+    if (group.registrationLevel == GroupRegistrationLevel.CLOSED)
+      return Text(tr("Closed registration"));
+
     return RichText(
       text: TextSpan(
           text: tr("Request membership"),