Describe the bug
Sometimes, songs appear multiple times when creating, duplicating or editing a setlist.

To Reproduce
Steps to reproduce the behavior:
Happens occasionally 🙈

Expected behavior
Songs must be unique per setlist.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
None.