'Input tensor dimension should be 3d' error when decoding Engine DJ stems

Denons Engine DJ recently got support for stem separation. The file the desktop software produces seems to be in STEMS format but there's something different in the format. The output of the `stem2files` utility with the file I attached (for demo I took a short snippet of a CC-BY-NC licensed track by "Timbre" which can be found [here](https://freesound.org/s/770565/)) is the following:

```
$ stem2files ./22\ e9f9eb56-b8cb-4669-a5a9-ac4235ae1983.stems
Traceback (most recent call last):
File "/Users/noir/projects/ng/./stems/bin/stem2files", line 8, in
sys.exit(cli())
^^^^^
File "/Users/noir/projects/ng/stempeg/stempeg/cli.py", line 69, in cli
stem2files(
File "/Users/noir/projects/ng/stempeg/stempeg/cli.py", line 110, in stem2files
write_stems(
File "/Users/noir/projects/ng/stempeg/stempeg/write.py", line 776, in write_stems
raise RuntimeError(f"Input tensor dimension should be 3d")
RuntimeError: Input tensor dimension should be 3d
```
I'm on MacOS 14.7.1 with ffmpeg 7.1.

The .stems file:
[22 e9f9eb56-b8cb-4669-a5a9-ac4235ae1983.stems.zip](https://github.com/user-attachments/files/18053639/22.e9f9eb56-b8cb-4669-a5a9-ac4235ae1983.stems.zip)