Playlist "Insert from queue" fails if playlist and queue contain a same track

Steps to reproduce

1. Add a track to a playlist
2. Add the same track to the queue
3. Try to add the queue to the playlist

What happens?

It seemingly loads indefinitely.

I could obtain this from the dev console:

POST
	
scheme
	https
host
	music.jfischer.org
filename
	/api/v1/playlists/5/add/
Address
	212.224.89.26:443
Status
400
Bad Request

What is expected?

Either an error message or even better, ignore the duplicates.

Context

Funkwhale version(s) affected: 1.1.4