MDL-9506 Issue 1: adjusting a gradeitem's value would result in a grade_final object...

MDL-9506 Issue 1: adjusting a gradeitem's value would result in a grade_final object with gradevalue assigned, even when a gradescale should have been assigned. Issue 2: double grade_final entries when calling grade_item->load_final() after grade_item->generate_final(). Issue 3: Calling grade_item->update_final_grade() without first calling grade_item->generate_final() would result in fatal error. generate_final() is now called if the raw and final arrays' sizes don't match.