message: Re-refactor UnitController.getUnitFor with orFail
diff: @@ -182,10 +182,7 @@ export class UnitController {
  }
  private async getUnitFor (unitId: string, currentUser: IUser, privilege: 'userCanViewCourse' | 'userCanEditCourse') {
  - const unit = await Unit.findById(unitId);
  - if (!unit) {
  - throw new NotFoundError();
  - }
  + const unit = await Unit.findById(unitId).orFail(new NotFoundError());
  const course = await Course.findById(unit._course);
  if (!course.checkPrivileges(currentUser)[privilege]) {
  