Fix `/until` crashing if the max rank has already been reached

[TimJentzsch]

Relevant issue: Closes #156

Description:

By default, the /until command takes the next rank as goal. However, if the maximum rank has already been reached, it would throw an error. Now, it will fall back to the next 10,000 tier.

Screenshots:

Checklist:

• [x] Code Quality
• [x] Pep-8
• [ ] Tests (if applicable)
• [x] Success Criteria Met
• [x] Inline Documentation
• [ ] Wiki Documentation (if applicable)