No institution - Default quota error

[Ghada El-Zoghbi]

Mahara: 16.04.1
OS: Linux
DB: Postgres
Browser: Firefox

The following error is generated the no-institution is saved with the following conditions:

* user is admin
* artefact : file : maxquotaenabled is set (Enforce a sitewide maximum quota = Yes)
* artefact : file : default quota is set (Maximum quota = set)

[WAR] fd (admin/users/institutions.php:661) Undefined index: defaultquota
Call stack (most recent first):

    log_message("Undefined index: defaultquota", 8, true, true, "/var/www/mahara-site-anu/admin/users/institutions....", 661) at /var/www/mahara-site-anu/lib/errors.php:489
    error(8, "Undefined index: defaultquota", "/var/www/mahara-site-anu/admin/users/institutions....", 661, array(size 5)) at /var/www/mahara-site-anu/admin/users/institutions.php:661
    institution_validate(object(Pieform), array(size 33)) at Unknown:0
    call_user_func_array("institution_validate", array(size 2)) at /var/www/mahara-site-anu/lib/pieforms/pieform.php:1429
    Pieform->validate(array(size 33)) at /var/www/mahara-site-anu/lib/pieforms/pieform.php:518
    Pieform->__construct(array(size 5)) at /var/www/mahara-site-anu/lib/pieforms/pieform.php:161
    Pieform::process(array(size 5)) at /var/www/mahara-site-anu/lib/mahara.php:4494
    pieform(array(size 5)) at /var/www/mahara-site-anu/admin/users/institutions.php:585

It needs to be wrapped with a check for the 'mahara' institution @ line 659:

    if (empty($institution) || $institution != 'mahara') {
        if ($USER->get('admin') || get_config_plugin('artefact', 'file', 'institutionaloverride')) {
            if (get_config_plugin('artefact', 'file', 'maxquotaenabled') && get_config_plugin('artefact', 'file', 'maxquota') < $values['defaultquota']) {
                $form->set_error('defaultquota', get_string('maxquotatoolow', 'artefact.file'));
            }
        }
    }