Old embed codes not working after update to 1.3.0

Steps to reproduce

1. Create an embed code using a pod that uses Funkwhale < 1.3.0. As an example, here it is one created in our instance, Baleafunk.eus, a year ago: <iframe src="https://baleafunk.eus/front/embed.html?&amp;type=track&amp;id=225" scrolling="no" width="100%" height="150" frameborder="no"></iframe> Note that the URL is /front/embed.html
2. Use that embed code in a website. For example: https://iametza.eus/saioa/hodeia-ez-da-existitzen-2x03-sakananet-sare-mankomunatua/
3. Update the pod to Funkwhale 1.3.0.

What happens?

The embedded player stops working. If I remove "/front" from the URL of the embed code, it works again. Funkwhale 1.3.0 creates embed codes with a URL that doesn't have that in the path: baleafunk.eus/embed.html?&type=track&id=225

What is expected?

The old embedded player should work after the update. It should be backwards compatible.

Context

Funkwhale version(s) affected: x.y

• Tested with Firefox and Chrome.
• Funkwhale 1.3.0, after updating from 1.2.8.
• Docker installation with nginx as a reverse proxy.
• I can reproduce the bug using various pods that use Funkwhale 1.2.8, 1.2.9 and 1.3.0.