Return a nice error message if searching for invitations by email finds no results

Description

1. Log in as admin
2. Go to https://archiveofourown.org/admin/invitations
3. In the "Enter all or part of an email address" field under Track Invitations, enter a nonexistent email.

What happens: nothing. If there's no result found, the page just stares at you blankly.

What should happen: it generates a message saying "No results were found. Try another search." if no matches are found.

Environment

None

Status

Assignee

Unassigned

Reporter

Nary Rising

Roadmap

Admin

Priority

Medium

Affects versions

0.9.252

Fix versions

None

Components

BackEnd

Difficulty

Medium

Required Access Level

Admin

Milestone

Internal 0.9