invite: Fix rendering invite modal for realms without default channels.

The default channels checkbox only exists in DOM if there are default
channels in the realm, so we should make sure that we check whether
there are default channels in the realm before accessing the
checkbox element in set_streams_to_join_visibility.

web/src/invite.ts

@@ -306,9 +306,11 @@ function set_custom_time_inputs_visibility(): void {
 }
 
 function set_streams_to_join_list_visibility(): void {
-    const default_streams_selected = $<HTMLInputElement>("input#invite_select_default_streams")[0]
-        .checked;
-    if (default_streams_selected) {
+    const realm_has_default_streams = stream_data.get_default_stream_ids().length !== 0;
+    const hide_streams_list =
+        realm_has_default_streams &&
+        $<HTMLInputElement>("input#invite_select_default_streams")[0].checked;
+    if (hide_streams_list) {
         $("#streams_to_add .invite-stream-controls").hide();
         $("#invite-stream-checkboxes").hide();
     } else {