MDL-32772: Change SQL for mod_assign gradingtable to use named query parameters
MDL-32772: Change SQL for mod_assign gradingtable to use named query parameters

This makes it consistent with the built in filtering in flexible_table.

Fix additional issue with SQL for grading table when there are no enrolled users

Change SQL for mod_assign grading table to use get_in_or_equal
As Suggested by Andrew Nicols in tracker

dilawar/moodle