Make site admin deal with new user course search

closes CORE-1603

Test Plan:
  - On staging or similar, go to <url>/accounts/site_admin/users
  - It should load

Change-Id: Ic4135510e7461dcea17dc350dea56f12bafe2bba
Reviewed-on: https://gerrit.instructure.com/155975


Reviewed-by: Brent Burgoyne <bburgoyne@instructure.com>
Tested-by: Jenkins
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Clay Diffrient <cdiffrient@instructure.com>

app/jsx/account_course_user_search/index.js

@@ -51,7 +51,7 @@ export default class AccountCourseUserSearch extends React.Component {
   render() {
     const tabList = this.props.store.getState().tabList
     const tabs = permissionFilter(tabList.tabs, this.props.permissions)
-    const ActivePane = tabs[tabList.selected].pane
+    const ActivePane = (tabs.length === 1) ? tabs[0].pane : tabs[tabList.selected].pane
 
     return (
       <ActivePane