stream settings: Fix scrollbar bug on unsubscribing themselves.

Fix scrollbar not updating when user unsubscribe themselves
from "Stream members" list, by clicking "Unsubscribe" button.

Fixes #9029

static/js/stream_edit.js

@@ -575,6 +575,7 @@ $(function () {
             }
             stream_subscription_info_elem.addClass('text-success')
                                          .removeClass('text-error');
+            ui.update_scrollbar($("#subscription_overlay .settings"));
         }
 
         function removal_failure() {