MDL-53300 core_grade: use currentgradetype if modgrade_type is not set
MDL-53300 core_grade: use currentgradetype if modgrade_type is not set

If mod has grades, then while upgrading
modgrade_type is disabled. This will not post
it with form and hence validation fails.
To avoid above problem, use ->currentgradetype
if modgrade_type is not set

dilawar/moodle