consider case when grade cutoff are letter

[melvinsoft]

Change description

When a course has a grade cutoff in letters, the new dashboard is failing, this is not that common, but it's affecting some users.

Type of change

• [x] Bug fix (fixes an issue)
• [ ] New feature (adds functionality)

Checklists

Development

• [x] Lint rules pass locally
• [x] Application changes have been tested thoroughly
• [x] Automated tests covering modified code pass

Security

• [x] Security impact of change has been considered
• [x] Code follows company security practices and guidelines

Code review

• [x] Pull request has a descriptive title and context useful to a reviewer. Screenshots or screencasts are attached as necessary
• [x] "Ready for review" label attached and reviewers assigned
• [ ] Changes have been reviewed by at least one other contributor
• [x] Pull request linked to task tracker where applicable