Manage groups page continues even though group does not exist

[Ghada El-Zoghbi]

Mahara: 20.10.1
OS: Linux
DB: Postgres
Browser: FF and Chrome

A user can bookmark a page for a group and come back to it at a later time after that group has been deleted.

The manage groups page should check that the group still exists and notify the user if doesn't find it.

To replicate:
1. Create a group 'AAA Test' from the page /group/edit
2. As a site admin, go to Administer groups (Admin > Groups > Administer groups)
3. Edit the group 'AAA Test' by clicking on the cog
4. Bookmark the page (for me it's: http://localhost/admin/groups/manage.php?id=283).
5. go back to the Administer groups page and delete the group 'AAA Test'
6. go to the bookmarked page for the deleted group

What should happen:
User should be notified that the group no longer exits

What currently happens:
Warnings appear that group could not be found with a call stack:

Call stack (most recent first):
log_message("Trying to get property 'quotaused' of non-object", 8, true, true, "/siteroot/htdocs/admin/groups/manage.php", 22) at /siteroot/htdocs/lib/errors.php:515
error(8, "Trying to get property 'quotaused' of non-object", "/siteroot/htdocs/admin/groups/manage.php", 22, array(size 58)) at /siteroot/htdocs/admin/groups/manage.php:22

and many more errors as the page continues to display.

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/11876

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/11876
Committed: https://git.mahara.org/mahara/mahara/commit/df0d0bd495a9df881939a3517b4f81bab8654471
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit df0d0bd495a9df881939a3517b4f81bab8654471
Author: Ghada El-Zoghbi <email address hidden>
Date: Wed Jul 28 10:02:56 2021 +1000

Bug 1938231: Check group exists before admin edit

Check the group still exists before continuing
to allow the edit of a group

behatnotneeded

Change-Id: I36efe9ca3f593936c296e55fb4aa6e64a0036440