bug#65765: Celluloid is broken

[Csepp]

Guix commit: d6966b8 (5 days old)
Trying to run celluloid results in this error:
celluloid: ../stream/stream.c:416: stream_create_with_args: Assertion 
`args->url' failed.

both celluloid and mpv are up to date according to guix refresh

It doesn't matter what arguments celluloid gets, the result always seems
to be the same.

I thought it had tests turned off, but no, it looks like its testsuite
is just very incomplete, because it definitely should have caught this.