Function get_in_or_equal does not accept empty arrays in local_o365 mode_maintenance_resyncgroupusers function

[patmr7]

In the case where synchronization is disabled for all courses, the get_in_or_equal function returns an error related to an empty array.

Coding error detected, it must be fixed by a programmer: moodle_database::get_in_or_equal() does not accept empty arrays

[More information about this error](https://docs.moodle.org/405/en/error/debug/codingerror)

Debug info:
Error code: codingerror×Dismiss this notification
Stack trace:
line 782 of /lib/dml/moodle_database.php: core\exception\coding_exception thrown
line 1435 of /local/o365/classes/page/acp.php: call to moodle_database->get_in_or_equal()
line 146 of /local/o365/classes/page/base.php: call to local_o365\page\acp->mode_maintenance_resyncgroupusers()
line 35 of /local/o365/acp.php: call to local_o365\page\base->run()