Adding track to playlist over Subsonic API will duplicate playlist

Steps to reproduce

Using Play:Sub (iOS) application:

• Add a track to an existing playlist (ID 1)

What happens?

• The track is added to a new playlist (ID 2)
• The playlist have the same name
• Both playlist ID 1 and ID 2 will now exist on the server and only playlist ID 2 will have new track

The same behaviour happens if the playlist is created from the Play:Sub app as well.

What is expected?

• The original playlist should be appended with the new song
• No new playlists should be created

Context

Funkwhale version(s) affected: 1.0

• Installed through Ansible (but with manual nginx configuration)
• Using custom HTTPS port